What ways are there to disrupt spellcasting in 5e?

[BoringInfoGuy]

Spot on. The game putting non-interruption as the default for reactions doesn't include an assumption that nobody's trying their best until the players split the right hairs.

Thank you

You're too late to act when they start. By the time your action is ready, they're already started. Characters in the fiction are not taking turns; they're all going at the same time. Initiative indicates who finishes a fraction of a second first.

If you want to act first (and win initiative), act on your turn. If you wait until another character's turn, your readied action takes place immediately they finish casting their spell (or whatever else you're reacting to).

This is a good point to build on. Since magic does not exist in real life, let’s use a different trigger to bypass the “magic works like x”, “no magic works like y” arguments.

A verbose enemy has been tossing insults against the party along with his attacks and orders to minions.

A couple of players have had enough of the insults.

One says:
“If he insults us again, I’m shooting him with a crossbow.”

The other says “If he starts insulting us again, I hit him with a crossbow.”

The trigger is a perceivable event.

The enemy says “All of you are fools”.

The DM ask both both players attacks if they want to use their readied actions after the insult is finished.

The second player complains that he said he was triggering off the start of the insult. So his attack should go off before the enemy finishes.

At what point did the insult start? The moment the enemy said “All...”.

But when could you TELL that it was an insult? Not at the moment when it first began. At that point, it could have been almost anything. “All of you are dead!” A threat. “All of you, take down the leader!” An order to minions. “All of this only delays the inevitable!” Villainous pontificating. “All I wanted was waffles!!!” Your villain is hungry / angry / crazy.

The start of the insult was the word “All,” but that is only recognizable in retrospect. The second player is trying to target a moment that could ONLY be identified AFTER that moment had already passed.

Now, apply that to using casting a spell as a trigger.

How do you identify the exact moment spell casting begins? Spells have a mixture of verbal, somatic, and material components. Not every spell used all three.

Is the wizard reaching for his component pouch or for a for a potion? Or maybe scratching an itch? Complicating the matter further, casters may be using a focus already in hand in place of a material focus. Is the wizard raising his staff because he is starting a spell and using it as a focus, or lifting it so it won’t drag on the ground as he prepares to move, or to point at who he wants his minion to attack, or is the he casting a spell without any material component at all?

Somatic gestures have the same problem. The wizard begins moving his hand. Is that the wizard starting the somatic gestures of a spell, reaching for a potion, flexing his fingers to loosen them up before he starts the actual somatic components, waving away a gnat, or just doing some random gesture as he chooses the target of his spell without a somatic component?

Ok, how about watching for the verbal component? Almost every spell as some verbal aspect. Still, not easy to note in real time. The wizard is starting to speak. When can you tell that the wizard is saying the words of a spell instead of preparing an insult, or giving orders to a minion, or simply talking to himself? Base it on the moment you hear a word you don’t recognize? Again, how do you know it is not a minion’s name or just a language you don’t speak? Or even if you do speak the language, if you are facing a human wizard and he says something in dwarfish, that could be enough to go “it’s not common - he’s casting!”

Casting a spell is a perceivable event. When someone begins to cast a spell is recognizable only in retrospect.

None of this is an attempt to say that you can’t perceive when someone is casting a spell. (Barring specific exceptions that we will for the moment ignore). Of course you can. So far I have not seen anyone dispute this.

And yes, an enemy casting a spell is certainly a valid trigger for a Readied Action. Again, I’ve seen no one dispute this.

But agreeing to this does not mean that we must also support the idea that you can make the trigger extra specific to override game mechanics. The beginning of something is not necessarily perceivable. Not in the moment at the time. It’s something you figure out when looking back.

Just because you add the word “begins” to your trigger does not force me to rule that your character has suddenly gained the ability to instantly recognize the exact moment the trigger started.

Something largely overlooked so far is that you DON’T have to use the Readied Action when the trigger occurs. There is a moment of decision where you can choose to not react to the trigger after all. This means that a moment exists between recognizing the trigger has happened and deciding to act on it. This works against the idea that a reaction is actually instantaneous.

There is nothing in the Rules As Written or the Rules As Intended to allow being extra specific on your wording will allow you to turn a reaction into an interruption.

“But JC tweeted he would allow a silence spell to be triggered off “Beginning to cast” and used to interrupt a spell being cast. This proves it was RAI.

Didn’t you see that Boring Info Guy?

Yes, I saw that. And I noticed some significant things about it.

1) He did not saw this was something that worked by RAW, but something he would allow as a DM

2) The tweet was from 2015.

3) Sage Advice Compendium was updated in January of 2019.

3a) A recent change in the latest Sage Advice Compendium is that not even JC’s tweets are considered official rule statements. The Sage Advice Compendium is now the ONLY source of official rulings for D&D 5e.

3b) While there are rule clarifications for the Ready action in Sage Advice, using a readied Silence to interrupt a spell and prevent it from taking effect is not included.

3c) Sage Advice talks about 3 rule viewpoints. Rules as Written, Rules as Intended, and Rules as Fun.

Having noted all this, it seems to me that the 2015 tweet was JC talking from a DM using the Rules as Fun perspective. The “I’m going to deliberately override RAW because I like the idea” approach.

Even if you disagree and want to argue that he instead meant it as a RAW / RAI statement, the fact that it is not in the current Sage Advice Compendium means it was later reconsidered and abandoned as a ruling.