What ways are there to disrupt spellcasting in 5e?

[CorporateSlave]

Is the window of opportunity between invoking a 1 action spell with a vocal and somatic component long enough to be interrupted by a guard pulling the trigger and having a crossbow bolt lodge into the wizards throat/hands? What about someone standing next to the wizard ready to restrain them/cup a hand over their mouth.

Here's the thing, you make this sound rhetorical (since that would support your position), but going by the RAW game mechanics, the answer is a firm "It depends on who wins Initiative."

Wizard, "I cast a spell!"
Guards, "We open fire!"
DM, "Everyone roll Initiative."
Obviously, neither side is Surprised.

Scenario 1: Guards win Initiative (theoretically at least, which would happen more often as Wizards on average could be expected to have lower Dex bonuses); they get their shots off. If the Wizard dies or goes unconscious, he cannot cast the spell and the guards have prevailed. If the wizard does not, he can cast his spell the same as any round of Combat where he takes damage early in the Round, before his Turn has come up.

Scenario 2: Wizard wins Initiative; he gets to cast his spell in its entirety, then the guards open fire. Again, just like any round of Combat where the wizard has rolled higher Initiative than someone else who wishes to attack him. ("not fair" because the Guards were at the ready? Initiative is a game mechanic to simulate the real world effect of who was 'quicker on the trigger.' If the Guards lose, the wizard is able to get his spell off just before they react and fire. That's what Initiative is. 5e isn't an episode of Jerry Springer, where whoever yells first and loudest 'wins.')

Scenario 3: The DM has decided to allow PC's and NPC's to use the Ready Action outside of Combat, and both Guards are considered to Ready their Actions to Attack on the trigger that "The wizard starts to cast a spell." The Guards win Initiative, see Scenario 1. Their Ready Action will not trigger, as their Turn has rolled back around before the trigger has occurred. However, they still get the first shot because they have won Initiative.

Scenario 4: The DM has decided to allow PC's and NPC's to use the Ready Action outside of Combat, and both Guards are considered to Ready their Actions to Attack on the trigger that "The wizard starts to cast a spell." The Wizard wins Initiative. He uses the Cast a Spell Action. The DM decides this allows the Guards to use their Reactions to Attack the Wizard; they get their shots off. If the Wizard dies or goes unconscious, he cannot cast the spell and the guards have prevailed. If the wizard does not, he can cast his spell the same as any round of Combat where he takes damage early in the Round, before his Turn has come up.

This scenario might be supported (very weakly) by RAW if combined with JC's ruling in the tweet (which isn't official if it hasn't made it into SA Compendium - admittedly I haven't checked this yet) about Turns outside of Combat. The (frankly, ridiculously rules-lawyered, system gaming) trigger has completed, but you can't rule that the Wizard's spell is disrupted or interrupted without a table or house ruling on this. The 5e RAW simply does not generally* sub-divide the casting of a 1 Action spell. If you think it does, please point me to the general* RAW reference regarding at what point a 1 Action casting time spell is far enough into casting that an attack would cause it to fail, yet still consume the spell slot (because unless this happens the Reaction isn't disrupting anything, it is pre-empting it)...because I have missed that bit. In any case, the Guards still gained a benefit here, as their Readied Action has given them one more attack against the wizard in the first round, as well as the chance to down him before he could cast the spell.

Scenario 5: The DM has decided to allow PC's and NPC's to use the Ready Action outside of Combat, and both Guards are considered to Ready their Actions to Attack on the trigger that "The wizard starts to cast a spell." The Wizard wins Initiative. He uses the Cast a Spell Action. The DM decides this allows the Guards to use their Reactions to interrupt the spell, due to the carefully worded trigger, ruling that this means they notice when the spell is in the process of being cast, but has not yet completed. It is now up to the DM to decide if this means the spell fails automatically or if he will allows the Wizard to make a CON save to continue casting. Fair enough, if that makes sense to him "realistically." However the DM rules...it is firmly in the territory of a table or house ruling, as there simply is no RAW support for allowing an attack to interrupt a spell as it is being cast. Plenty of common sense reasons, fine. Ways to infer it from other things such as Counterspell...ok...but none in a way that goes along with the core 5e philosophy of "specific beats general*." But 5e RAW only addresses a couple of specific exceptions that allow an interruption.

*You need not bother to site how Counterspell works, because I've yet to read an argument about why in the RAW a specific spell's rules should apply generally to all similar situations...effectively turning "Specific beats general" into "Specific becomes general."

If it makes "realistic sense" to you then go for it...but recognize it is a table ruling based on what you've decided makes sense, and not 5e RAW...which I believe puts this limitation on the Ready Action quite intentionally. Part of the reason I believe this is that it is so easy to "common sense" around it! And that it used to exist in earlier editions! How can its omission be other than intentional for some game balance purpose? I would certainly be interested to hear what Crawford has to say on the RAI on this issue.

[Max_Killjoy]

Nope. It says that when the trigger occurs, you are allowed to take your reaction. That reaction, however, happens after the trigger finishes.

"When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger."

It's not just "after the trigger", but "after the trigger finishes".

That's why you can't go "in between".

So what if you do set the trigger as a particular casting a spell, and then that opponent casts a spell with a multi-round casting time?

Are you stuck waiting for the casting to finish, frozen there waiting for their "action" to finish?

[CorporateSlave]

Ready action asks for a perceivable trigger. This rule tells us when the casting of a spell is perceivable.

Every other argument, is just their view of the game and not RAW.

The rule tells us the casting of a spell is perceivable. It does not in any way sub-divide the perceivable casting of a 1 Action casting time spell into smaller, discrete perceivable units.

If anything, the RAW here damages the argument that you can declare a Ready Action trigger as "when the wizard begins to cast a spell." The spell casting rules in XGTE state that it is perceivable that a spell is being cast if it has V, S, or M components, it doesn't break that down at all into beginning, middle, or end. As the RAW here goes, the trigger would have to then simply be "if the wizard casts a spell," as that is what it says can be perceived. Per the RAW in the PHB regarding the Ready Action, this trigger (the perceivable casting of a spell) would complete prior to the Ready Action being used.

[ThePolarBear]

So what if you do set the trigger as a particular casting a spell, and then that opponent casts a spell with a multi-round casting time?

Are you stuck waiting for the casting to finish, frozen there waiting for their "action" to finish?

By the rules? Yes. Edit: at least until the beginning of your next turn.

[Rukelnikov]

Nope. It says that when the trigger occurs, you are allowed to take your reaction. That reaction, however, happens after the trigger finishes.

"When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger."

It's not just "after the trigger", but "after the trigger finishes".

That's why you can't go "in between".

My argument is that by RAW, the readied action comes after the trigger. Not only is that the rule, it also makes sense to me that it would work that way.

In neither case does it say that you finish identifying the spell before the caster finishes casting it. Both cases are also completely unrelated to the Ready action, which specifically takes place after the trigger, not during it. A reaction works the way the rules say that it works; it doesn't work the way the rules say some other, completely different, reaction does.

After the trigger, which I define.

Casts a spell is not my trigger, starts casting is. Once someone starts casting, my trigger is finished.

[CorporateSlave]

So what if you do set the trigger as a particular casting a spell, and then that opponent casts a spell with a multi-round casting time?

Are you stuck waiting for the casting to finish, frozen there waiting for their "action" to finish?

The PHB does have RAW describing how casting a spell with multiple round casting time is handled, and how it can be disrupted.

But the short answer is yes, you would have to wait until the caster has spent their entire Action towards casting the spell for your trigger to be considered completed.

Your trigger is "casting a spell."*
The caster has spent an Action to Cast a Spell.
Your trigger is finished. The spell itself is not complete unfortunately for the caster, but his Action has been used to Cast A Spell. It's just that acceding to the RAW, a longer casting duration requires you to take the "Cast A Spell" Action every Turn until the process is complete for the spell to be completed.

*yes, I see the inevitable semantics debate. But trying to expand the argument by giving an example of a multiple turn casting time spell is irrelevant, as that is addressed in the RAW, and is acknowledged as its own "thing" so to speak.

[ThePolarBear]

After the trigger, which I define.

Casts a spell is not my trigger, starts casting is. Once someone starts casting, my trigger is finished.

But if "start casting" is your trigger, than you can't rely on "casting a spell" being perceivable, and need to provide why "start" is a perceivable occurrence.

Edit: it also has to finish. Which is, incredibly, related to the thing that is "starting". Because otherwise, you'll need a lot of explaining how something abstract "begins" or "finishes".

[Rukelnikov]

But if "start casting" is your trigger, than you can't rely on "casting a spell" being perceivable, and need to provide why "start" is a perceivable occurrence.

If I can perceive a casting is taking place, then it has already started.

[Max_Killjoy]

The PHB does have RAW describing how casting a spell with multiple round casting time is handled, and how it can be disrupted.

But the short answer is yes, you would have to wait until the caster has spent their entire Action towards casting the spell for your trigger to be considered completed.

Your trigger is "casting a spell."
The caster has spent an Action to Cast a Spell.
Your trigger is finished. The spell itself is not complete unfortunately for the caster, but his Action has been used to Cast A Spell. It's just that acceding to the RAW, a longer casting duration requires you to take the "Cast A Spell" Action every Turn until the process is complete for the spell to be completed.

So this is an exception to the stated rule that the "trigger" has to be completed before the reaction can happen -- the caster has not, in fact, completed casting their spell.

[JoeJ]

After the trigger, which I define.

Casts a spell is not my trigger, starts casting is. Once someone starts casting, my trigger is finished.

There's no difference. Regardless of how you phrase it, what you perceive is somebody casting a spell. When they finish, you go.

There is no provision in the rules for taking a Ready action after a trigger has started but not finished. At all. If your trigger is, "if the orc starts to throw a punch," you'll go after the punch hits or misses. If it's "if the wizard starts to take a step," you go after they take the step.

[ThePolarBear]

If I can perceive a casting is taking place, then it has already started.

Then you just demonstrated that you cannot perceive it start. You can deduce it has started because you are perceiving that the casting is ongoing. And you have to wait for it to finish. Because what you are perceiving is the current act of casting a spell, and that's actually the perceivable occurrence.

QED, something like pages ago.

[CorporateSlave]

So this is an exception to the stated rule that the "trigger" has to be completed before the reaction can happen -- the caster has not, in fact, completed casting their spell.

Nice try, but if you were foolish enough to make your trigger "finish casting a spell" rather than just "casting a spell" then yes, your would not be able to use your Reaction as you would be waiting for the spell to complete. Of course, being that it will take several turns, you can just use your Action to Attack and try to break Concentration, just like it says in the RAW about longer duration spells being cast in combat.

The point is, the game mechanics don't allow the interruption of a 1 Action casting time spell except by specific exceptions (like Counterspell), no matter how you might chose to rules lawyer a trigger phrase. Its rather disingenuous to try and expand the longer casting time rule to cover 1 Action spells.

Trigger "I attack if the wizard casts a spell." (Something that is perceivable per the DM section of XGTE) The wizard uses his Action to Cast a Spell (unless there is another way to use your Action casting a spell?). The Action is completed, "Cast a Spell" has been satisfied. The trouble for the wizard is, for longer casting times one Action worth of Cast A Spell completed doesn't actually complete the spell.

Look I get it doesn't make sense when broken down and looked at from all angles - but you can always twist words and meanings and come up with hypothetical "what if" situations that will support any given view. But 5e rules are simplifications that streamline the chaos of the real world into easy to follow Rounds and Turns. Sometimes these rules grant this simplification at the cost of common sense from certain points of view. That's why DM's can make table rulings, and why we have house rules.


If you want to (as some here have inferred) the ridiculousness of this entire debate, perhaps consider that the OP actually acknowledges in his original post that using an attack to disrupt a spell no longer exists in 5e, and he is looking for feats or abilities beyond Counterspell that might allow it. 14 pages so far that you guys who think it makes sense could have just said, "well there's not much in the 5e RAW, but just house rule that it still works, and force a Concentration check or something."

[Rukelnikov]

Then you just demonstrated that you cannot perceive it start. You can deduce it has started because you are perceiving that the casting is ongoing. And you have to wait for it to finish. Because what you are perceiving is the current act of casting a spell, and that's actually the perceivable occurrence.

QED, something like pages ago.

I can perceive the caster going for the component pouch, or speaking unintelligible words. Triggers can be deductive "If someone hurts me I use second wind", a hidden rogue sneaks me, I didn't see it happen, but i'm hurting I get to use second wind.

[JoeJ]

I can perceive the caster going for the component pouch, or speaking unintelligible words. Triggers can be deductive "If someone hurts me I use second wind", a hidden rogue sneaks me, I didn't see it happen, but i'm hurting I get to use second wind.

You can only perceive a person doing something that they have already started doing.

Looking for a moment only at the fiction level, let's say you plan to do something if the druid starts casting a spell. What does that mean? At some point her hand starts to move and/or she starts uttering sounds. You can't perceive either until her hand has already moved and/or sounds have been uttered. At some later point you have perceived enough movements and/or sounds to make a judgment that she is, in fact, casting a spell. At that point you can start doing whatever it is you planned to do. Whether or not you can do it in time to interrupt her depends on how long it takes her to cast the spell, how long it takes you to do your thing, and how quick your reflexes are.

None of those vital bits of information are known at the game level. Without that information it's impossible to calculate whether or not you would "realistically" be able to interrupt her spell. So the game doesn't try; it simply abstracts and makes the universal judgment that no, you are not quick enough to use a readied action that interrupts whatever triggered it.

[Max_Killjoy]

Nice try, but if you were foolish enough to make your trigger "finish casting a spell" rather than just "casting a spell" then yes, your would not be able to use your Reaction as you would be waiting for the spell to complete. Of course, being that it will take several turns, you can just use your Action to Attack and try to break Concentration, just like it says in the RAW about longer duration spells being cast in combat.

Some posters have claimed that the if trigger for the Reaction is "that guy casts a spell", then the Reaction can't happen until the spell casting has finished.

No one said anything about making the trigger "finish casting a spell", other than those posters.

The point is, the game mechanics don't allow the interruption of a 1 Action casting time spell except by specific exceptions (like Counterspell), no matter how you might chose to rules lawyer a trigger phrase. Its rather disingenuous to try and expand the longer casting time rule to cover 1 Action spells.

As I said early regarding the charge of "rules lawyering":

I'd turn that on it's head and say that the reason players feel the need to make that argument* is that the rules, at least as some here are saying, force them to, via the contrivance of "you can't react until the trigger is completely finished, and only in-system atomic events are triggers in combat".

* "that argument" being that they can refine the phrasing enough to trigger on the start of an enemy action, rather than its completion.

[CorporateSlave]

I can perceive the caster going for the component pouch, or speaking unintelligible words. Triggers can be deductive "If someone hurts me I use second wind", a hidden rogue sneaks me, I didn't see it happen, but i'm hurting I get to use second wind.

So you're saying if the trigger is "someone starts to hurt me" I could use Second Wind before all the damage is applied, interrupting the attack? Break the damage in half somehow? Logically, I could be pulling back as the blade begins to cut me, at that first hint of pain.

Or should you be able to say, "If I see the archer starting to shoot at me (or the dragon starting to breathe at me, or the Beholder starting to look at me with its eyestalks), I Move behind total cover?" If all this is supposed to work, why the devil even say the trigger needs to finish? Just to "gotcha!" players who forget to add the "starting" rider to their trigger in any of the above circumstances, or a million others just like them where a player uses tricksy wording to try and short circuit the rules and thereby amplify the power of the Ready Action a hundred fold?

You can make the trigger's wording as pin point as you want, I'm not getting drawn in to a hypotheticals debate where you can frame the "real world" situation in a way that twists it to your advantage. Its just not what the rules say. There is nothing except a couple of specific exceptions that allow interruption of a spell being cast in 5e, period. Its a game mechanic, and there is no indication it is not intentional. All sorts of rules do not make perfect real world sense, but the rules are as such for game balance. Just house rule it however you want at your table, nobody cares. But your common sense house rules are not the official 5e RAW, no matter how "real world" logical you may think they are.

Normally Readied weapon attacks do not disrupt 1 Action spells being cast in combat. No matter what the trigger, any DM trying to follow the RAW would still allow the spell to be cast before the effects of the Readied Action are applied, because nowhere in the RAW does it say otherwise.

[JoeJ]

So what if you do set the trigger as a particular casting a spell, and then that opponent casts a spell with a multi-round casting time?

Are you stuck waiting for the casting to finish, frozen there waiting for their "action" to finish?

I don't think the devs. considered the case of somebody casting a multi-action spell in combat*. RAW, you can't use the readied action so you'd lose it (along with the spell slot, if that's what you had readied) at the beginning of your next turn. However, in this case I would allow you to take your readied action and count it as taking place after the caster has spent their action casting (if, for some reason, the timing mattered).

(edit: *in respect to the Ready action).

[Tanarii]

I can perceive the caster going for the component pouch, or speaking unintelligible words. Triggers can be deductive "If someone hurts me I use second wind", a hidden rogue sneaks me, I didn't see it happen, but i'm hurting I get to use second wind.

The first is not starting to cast a spell. That's a trigger of reaching for the component pouch. If you somehow interrupt it, they aren't yet casting a spell, so they are free to do whatever they like with their action. Within their capabilities, based on how you interrupted it.

The second has no distinguishable line between perceiving "starts casting a spell" and "casting a spell". So either way you must wait until they finish casting the spell.

[CorporateSlave]

Some posters have claimed that the if trigger for the Reaction is "that guy casts a spell", then the Reaction can't happen until the spell casting has finished.

No one said anything about making the trigger "finish casting a spell", other than those posters.

It should be fairly obvious that those posters were talking about 1 Action (or less) casting time spells, as the rules for longer casting times are completely different, and quite interruptible. If any of us were talking about interrupting spells with a longer casting time, the debate would have been over with the first post that cited the "Longer Casting Times" text from the PHB.

So assuming you were just asking a totally innocent question, I did give a straightforward answer regarding the Longer Casting Time rules and how it would function as RAW...but that it is not even remotely the same situation. You then replied:

So this is an exception to the stated rule that the "trigger" has to be completed before the reaction can happen -- the caster has not, in fact, completed casting their spell.

Given from your carefully worded posts you are clearly not an idiot, I find it impossible to believe you are unable to understand the difference between an "exception" to a rule, and a completely different rule that acts in a completely different way.

It is a clever spin game, using Longer Casting Time to try and refute that a 1 Action casting time spell cannot be sub-divided into beginning/casting/finished...but those are completely different rules. (Not that they even divide a spell into beginning, middle, and end...they just draw the casting time out over many Actions, with Concentration needed in between.) Even if that opens up the debate about how a "the wizard casts a spell" applies towards a wizard using the Cast A Spell Action over and over to cast a Longer Casting Time spell as a Ready Action trigger, it does not affect the RAW game mechanics of a 1 Action spell. Two separate rules, two separate questions.

It may seem strange or unnatural to some, but common sense does not always apply when it comes to game rules, and that is often by design.

Regarding rules lawyering...I'm sure the reason players want to make the argument that they can interrupt a spell being cast with an attack is indeed that they don't like that this option was removed from the 5e rules (after being explicitly present in past editions). But its still rules lawyering.

Also, everyone: I am still waiting for a good answer from anyone to the following:

Please cite where it states that a specific spell description's ability should apply to a general situation, counter to 5e's PHB Introduction that states "specific beats general." (the "since Coutnerspell allows you to interrupt, it means anything should allow you to interrupt" argument)

Why they believe the ability to attack and interrupt a 1 Action or less casting time spell is meant to be included in 5e even though it was explicitly described in earlier editions but has been left out of 5e's RAW. One sentence (either under Ready Action or Casting a Spell) could have clarified how this would work. It's not a new idea. It is there for Longer Casting Time spells! Why isn't it stated in the RAW for 1 Action casting time spells?

[Naanomi]

One of the problems is that spell casting clearly isn’t instant... there is waving of hands, manipulating material components, chanting... it isn’t ‘snap’ and done, it takes some time... and in that time is it interactable? The rules give little guidance on it, and I presume the default is ‘no’

But... what about other actions that only take one round? Can I be a cow-boy and shoot someone ‘if they reach for their weapon’? Reaching for a weapon is part of an attack action, which only takes one round...

Can a guard attack someone ‘who starts to struggle with their bonds’? Escaping bonds may only take one action, thus even the most diligent guard can only attack people once they escape...

And, to go back to an earlier point, what if I am a telepath? Is ‘commuting mentally to cast a spell’ a valid trigger that can preempt the actual cast attempt?

[Rukelnikov]

You can only perceive a person doing something that they have already started doing.

That's exactly the point, saying begins casting a spell, means it triggers once they started, since I can't perceive it beforehand (unless I have foresight I guess)

Looking for a moment only at the fiction level, let's say you plan to do something if the druid starts casting a spell. What does that mean? At some point her hand starts to move and/or she starts uttering sounds. You can't perceive either until her hand has already moved and/or sounds have been uttered. At some later point you have perceived enough movements and/or sounds to make a judgment that she is, in fact, casting a spell. At that point you can start doing whatever it is you planned to do. Whether or not you can do it in time to interrupt her depends on how long it takes her to cast the spell, how long it takes you to do your thing, and how quick your reflexes are.

None of those vital bits of information are known at the game level. Without that information it's impossible to calculate whether or not you would "realistically" be able to interrupt her spell. So the game doesn't try; it simply abstracts and makes the universal judgment that no, you are not quick enough to use a readied action that interrupts whatever triggered it.

For the records, I'm not saying attacking them mid-cast will disrupt the spell. Aside from that, a reaction is "an instant response to a trigger of some kind" (PHB 190), so it should be "faster" than an action, I don't think that's worth arguing though, since it wouldn't change much in the current discussion.

The first is not starting to cast a spell. That's a trigger of reaching for the component pouch. If you somehow interrupt it, they aren't yet casting a spell, so they are free to do whatever they like with their action. Within their capabilities, based on how you interrupted it.

The second has no distinguishable line between perceiving "starts casting a spell" and "casting a spell". So either way you must wait until they finish casting the spell.

So if my trigger is when X starts talking, I have to wait until they finish saying their piece ?

[JoeJ]

One of the problems is that spell casting clearly isn’t instant... there is waving of hands, manipulating material components, chanting... it isn’t ‘snap’ and done, it takes some time... and in that time is it interactable? The rules give little guidance on it, and I presume the default is ‘no’

But... what about other actions that only take one round? Can I be a cow-boy and shoot someone ‘if they reach for their weapon’? Reaching for a weapon is part of an attack action, which only takes one round...

Can a guard attack someone ‘who starts to struggle with their bonds’? Escaping bonds may only take one action, thus even the most diligent guard can only attack people once they escape...

And, to go back to an earlier point, what if I am a telepath? Is ‘commuting mentally to cast a spell’ a valid trigger that can preempt the actual cast attempt?

You can certainly do those things, but you don't use the Ready action to do them. You do them by winning Initiative.

[PhoenixPhyre]

I've put a personal take on this whole issue (and many others like it) in a spoiler. This is me as a DM, not even really looking at the text of this particular case (hence the spoiler).

Spoiler: Personal take, non-text focused

Show

Whenever I hear phrases like "well, if I word it like so" or "all you have to do is phrase it correctly...", my munchkin detector goes off and I immediately suspect that whatever is being proposed violates at least the spirit of the rules and is being proposed for unwarranted personal gain. And if the result is that they get something valuable for a much smaller price than similar class features or spells, especially if by doing so they avoid paying any long-term resources...that's a huge red flag. And when it's backed up with out-of-context quotes to other specific rules or to "realism" or "common sense" (which usually isn't warranted), that's a whole chorus of alarms. Throw in "but the rules don't say I can't", and you have the perfect storm of self-interested rules abuse.

That kind of loophole hunting may be acceptable elsewhere, but not at any table I'm willing to be at. And nothing in the design of 5e encourages it. It's not just rules lawyering, it's bad rules lawyering, with the intent to gain extra unwarranted power for yourself. It is "magic word" thinking that would get a lawyer reprimanded by the court.

I'm pretty lax with the rules, most of the time. I let people take bonus actions whenever (despite what the rules say, I don't care enough to police it). I let people stretch the plausible boundaries, as long as they're working in the framework of the fiction and not trying to abuse things. This kind of "cleverness" turns me cold and I will go out of my way to stomp it out. Usually by giving the player a warning that if they try anything like that again, they will be asked to leave. Use the rules to act in the game, don't try to find "clever" hacks for personal gain at the expense of everyone else, including their time. Because these sorts of things always require lots of table time and arguments over minutia, for no wide-spread benefit.

I'll handle edge cases where it fits the fiction exactly as they are, edge cases. Each one will get considered on its own merits, not as some kind of blanket permission. And you'll get a lot further with me by not appealing to careful wording or rules. Telling me "I know this is technically not allowed, but can I <do X>, because <Y in-fiction reasons>" will get me to at least consider it for this once. Coming at me with "the rules say I can <do X> if I carefully phrase it as <A> and..." will get a flat no and a warning. I hate when people try to use rules as weapons to force others to accept your will or shields to deflect accusations of unfun behavior.

[CorporateSlave]

One of the problems is that spell casting clearly isn’t instant... there is waving of hands, manipulating material components, chanting... it isn’t ‘snap’ and done, it takes some time... and in that time is it interactable? The rules give little guidance on it, and I presume the default is ‘no’

But... what about other actions that only take one round? Can I be a cow-boy and shoot someone ‘if they reach for their weapon’? Reaching for a weapon is part of an attack action, which only takes one round...

Can a guard attack someone ‘who starts to struggle with their bonds’? Escaping bonds may only take one action, thus even the most diligent guard can only attack people once they escape...

And, to go back to an earlier point, what if I am a telepath? Is ‘commuting mentally to cast a spell’ a valid trigger that can preempt the actual cast attempt?

By RAW, the answer to most of those is; Sure they are viable Ready Action triggers. But yes you have to wait until the Action is over to React. Trying to apply "real world" logic to rules created for game balance is always going to bring about "WTF" moments. But first of all consider, just because a Reaction doesn't mean you can automatically interrupt the Action doesn't mean it is worthless or meaningless. You still get to make your attack (or whatever) outside the normal sequence of Initiative. How big an impact this might have varies greatly, of course.

Spell casting - you can use Counterspell to React and counter a Counterspell, itself a Reaction, right? And a spell with a casting time of 1 Reaction is, per RAW, "These spells take a fraction of a second to bring about..." It just isn't about timing, its about rules and game balance. 5e isn't designed to allow anything to interrupt 1 Action spells besides certain explicit exceptions.

Shoot someone who reaches for their weapon? Sure. But if that drawing the weapon is done per the PHB "as part of an attack" then the attack would resolve first.

Prisoner struggling with their bonds? You can attack, although they might succeed at breaking out of them first.

If you need to think of everything in real world terms, don't just imagine the prisoner struggling with their bonds for 6 seconds while the guard stares on, slack jawed. It's a game. The narrative can follow the mechanics, it doesn't have to be the other way around. "You struggle against your bonds, suddenly breaking free! Unfortunately, the guard as been watching, and although it took him a moment to figure out what you were doing, the moment after you break free he swings at you!"

[JoeJ]

That's exactly the point, saying begins casting a spell, means it triggers once they started, since I can't perceive it beforehand (unless I have foresight I guess)

You also can't react infinitely fast. Or, in this cast, fast enough to do what you're claiming.

[Rukelnikov]

You also can't react infinitely fast. Or, in this cast, fast enough to do what you're claiming.

Funny thing, according to PHB it is instant ("instant response to a trigger of some kind")

[Aimeryan]

Interesting. I've read the entire thread; those who can only see atomic actions still only see atomic actions, those that see interruptible actions still only see interruptible actions. I don't really see this changing. That said, the thread isn't really for those who already have strong opinions, its for those who don't.

Personally, I've been convinced that the trigger for a Ready action is not an atomic action; no evidence has been provided for such an assertion. That said, I see only some edge cases where it might actually come into play inside of combat. Movement is a far easier trigger to see a useful application for - 'comes into range', for example.

I also have not seen any evidence that a player or npc could not ready outside of combat. However, as stated in the PHB, outside of combat things are not so structured and defined. Essentially, it is left more up the DM to determine what can be done, and how - there is no RAW to work from here. The general scenario of 'if they make a move I'll shoot' should be covered by most reasonable DMs, I feel - whether that is via the Ready action or something less structured is up to the DM.

[JoeJ]

Funny thing, according to PHB it is instant ("instant response to a trigger of some kind")

Is that the same PHB that says a readied action happens after the trigger finishes?

[NaughtyTiger]

So far, everyone agrees that:

On the first round of combat,

• if a character is not surprised, the character knows which creature(s) initiated combat and by which action (attack, cast a spell, ..), but not their target or intent.
• if a character is not surprised and has higher initiative than the creature(s) that initiated combat, then that character may attack the creature(s) that initiated combat.
• if a character is not surprised and has higher initiative than the creature(s) that initiated combat by casting a spell, then that character may attack the caster after starting the spell but before finishing.

(you all have convinced me that I was being a bad DM by not telling the players that they knew what started combat)

Adversarial DMs can cheat the system. Adversarial players can try to cheat the system.

We disagree on:
on subsequent rounds of combat,

• that the character knows which creature(s) are performing what action
• that the character with higher initiative may attack the creature(s) start an attack but before finishing (using Ready Action)
• that the character with higher initiative may attack the caster after starting a spell but before finishing (using Ready Action)

DMs who argue in favor of players using Ready Action at the start of the spell are being adversarial against themselves (and munchkining) and cheating the system.

JoeJ's version of the narrative is that all creatures are starting their actions at the same time in a round of combat (initiative determines who finishes first). Thus every involved creature has started their action at the top of the round (including casting a spell). That meshes pretty well with my narrative.

We differ in that, I say the faster creatures can identify which slower creatures are performing which action and can choose to attack based on that (using Ready Action).

All the insistence that characters know the attacker and action on the first round of combat (by everyone) and the narratives (from everyone) have strengthened this interpretation of the rules for me.

So, thanks.

[Cybren]

By RAW, the answer to most of those is; Sure they are viable Ready Action triggers. But yes you have to wait until the Action is over to React. Trying to apply "real world" logic to rules created for game balance is always going to bring about "WTF" moments. But first of all consider, just because a Reaction doesn't mean you can automatically interrupt the Action doesn't mean it is worthless or meaningless. You still get to make your attack (or whatever) outside the normal sequence of Initiative. How big an impact this might have varies greatly, of course.

Except readied actions don't care about actions as the trigger. They care about perceptible events. Similar to Naanomi's examples, "I shoot them with my crossbow as they begin talking" shouldn't mean that you have to wait for them to complete a paragraph? Once they begin vocalizing the trigger has occured.

The problem here with "reacting to beginning casting a spell" seems to me that the less information you have, the less sure you are that you're reacting to the correct thing. "starts to cast a spell" probably visually reads similar to "flips the bird" or "talks with exaggerated hand gestures".