What ways are there to disrupt spellcasting in 5e?

[ProsecutorGodot]

But the absurdity is solely about the content - it's unrelated to the readied action, so it doesn't prove anything (except, maybe, that you've run out of valid arguments.)

(first off, apologies for dredging up a comment so far down in the thread, I haven't had the chance to reply until now)
I made the content absurd because the context allowed me to do so.

That's the problem. You didn't even argue that the DM wouldn't be allowed to do something so absurd like this, you instead argued against "why" he would do something like this. Because he can, under such an interpretation, just to be smart and obnoxious towards his players.

Just like players who would try such a thing are only being smart and obnoxious towards their DM.

You could have just as easily have said "what if the DM gives their NPCs a magic item that can instantly annihilate anyone with no save. Then the NPC takes a readied action and uses it. Isn't that ridiculous?" Yes, yes it is. But it has nothing to do with readied actions. If you want to discuss whether using multiple high-level casters with Finger of Death is fair to the PCs, start a separate thread, don't change the subject to something unrelated like that.

Again, the content of the example is irrelevant. The point was to illustrate that allowing such a trigger for reactions is absurd, looks absurd in practice and makes even players in defense of such a trigger see the extreme as absurd.

If those in defense of this practice are seeing the end result of allowing such a ruling (and this is only the most absurd end result that I could see, there is likely even more absurd scenarios that would be enabled by this) then you're advocating for the doom of your tables enjoyment on this one. People are going to be fighting about how their careful contract-like wording was more precise than the DM's and no one is going to get anything done.

Well, it's definitely not metagaming! You clearly understand the difference in outcomes. "If they reach for their spell component, I do X" is an entirely reasonable, in-universe action a player could logically take in the setting; it's also clearly supported by the rules (and is clearly intended to be supported by the rules!) You're the one who's trying to metagame up some sort of complex reason why it isn't allowed - the DM says "with a readied action, the necromancer interrupts you to..." and you're getting up in his face playing rules-lawyer to prevent it.

It certainly is metagaming to be reacting to a trigger that would start initiative before the initiative has started. It's definitely metagaming to think that your players choice of wording can influence your characters reaction speed to be infinitely fast. Your players wording should not affect your characters abilities if that wording is in direct conflict with both the rules and fiction. If adding "begins" to the trigger is enough to make you react faster in the fiction, everyone would do that to start with and the fact that you are meant to react to and not pre-empt those triggers would be pointless.

"If they reach for their spell component, I do X" is arguably the most reasonable version of this that I've seen proposed yet. You don't know the NPC is casting a spell by reaching for this however and a tricky DM could twist that wording in a way that you never see such a trigger either "they didn't reach for their spell components, they were already in hand (or the spell is only vocal, or somatic, or cast from an item with isn't a component"

Which he would be absolutely within his right to do, if you're arguing that hair-splitting semantics are necessary to achieve a result, your DM can do that as well. You're not going to be happy when he does.

It is useful in certain extremely specific situations (eg. if you're waiting to see what the enemy does, and don't want to act if they do something unexpected.) There's no reason to penalize player creativity by trying to bar it from being used in those situations, especially since first, we know from the Sage Advice answer that interrupting people with a readied action is RAI, second, you've repeatedly failed to come up with either a RAW reason to ban it (unsurprising since it's RAI), and third, you've repeatedly failed to demonstrate any problems that would emerge from allowing it.

If your DM has had you roll initiative in a situation where you aren't sure that the opposition is a threat, you shouldn't have rolled initiative to begin with. If you're attempting to use a similar strategy out of combat, you would determine whether the target was surprised, roll initiative and if they were surprised the outcome would happen exactly as you intended. If they weren't surprised and you rolled higher than them, they could react. If they weren't surprsied and they rolled higher than you, you didn't actually manage to surprise them AND they were faster than you expected. These results all make sense in the fiction.

See above for the example of problems that would arise.

Your arguments are completely incoherent - you swing wildly from "it's overpowered and if you allow it people would do it constantly if they knew they could" to "it's useless and therefore there's no reason to do it." You have to pick one of those two, you can't argue both. (And if you pick the second, as I think you're aware, you've immediately conceded the debate in any practical sense, since it's silly to bar players from doing something completely harmless when we have a Sage Advice suggesting you allow it.)

Whereas the argument to just follow RAI and allow it is extremely straightforward and obvious - it doesn't break anything, it doesn't cause any problems, and players may occasionally be able to find clever ways to use it to take advantage of specific situations where they want to delay their action. Obviously it's situational - readied actions are generally situational - but I don't see the reason to be so opposed to it.

First off, I am on record in this thread for advocating a case by case exception to be made. However, we have no evidence that Ready Action is meant the same allowance as War Magic and Shield Master. Claiming that different reactions shape the intended use of Ready Action isn't accurate.

Second, it's true that if you allow people with the knowledge to do it constantly that it becomes useless. When this has become the general rule at your table your DM is just going to change the rules in a way that doesn't end up aggravating the situation further.

It's overpowered in the sense that people seem to believe that the "cost" of an Action and Reaction is comparable to the "cost" that a spellcaster would have taken to know/use counterspell. Sorcerers sacrifice one of their few spells known, Bards must pick it up using magical secrets, Wizards have to prepare it, Paladins can only acquire it through a single subclass and Rangers can't even get counterspell naturally, they only get a similar effect at level 11 of a specific subclass (which is a deep dive into Ranger, since most campaigns don't stretch past levels 13-16)

But if a readied action Arrow is an effective method of counterspelling, why would any of those spellcasting classes bother.

It's also true that in the vast majority of situations, you could word your Readied Action in a way that doesn't require an interrupt and do the same thing - eg. the "cast when they move next to you, not when they attack" example. But if you require that then you are playing rules-lawyer and demanding metagaming from your players in the wording of their readied actions, aren't you? "I ready an action if someone moves to attack me" is straightforward, clear, and fits the rules.

Whereas "I want to react if someone seems about to attack me" vs. "I want to react after someone attacks me" is an extremely straightforward and obvious distinction that fits the rules as written.

Reacting to movement is a good trigger because movement is incremental. You can interrupt their move easily, both in the rules and in fiction. You can't, however, easily interrupt their action in the same way. There's no evidence to suggest that actions have incremental step processes that can be interrupted in a way that would prevent them from resolving. Movement resolves as soon as you reach the new space.

When you set a trigger "I ready an action if someone moves to attack me" your trigger reads to the DM as "I ready an action if someone moves within a range to attack me" your character doesn't know the difference just because you know the difference as a player.

Likewise, when you set a trigger "I want to react if someone seems about to attack me" is pointless because at this point you're in an initiative order, which should mean that if you are properly in initiative, there are several creatures that already seem like they're about to attack you. You could have taken your action instead.

Telling them "no, it has to be if the enemy moves next to you, because by my interpretation interrupting an action like that isn't allowed" adds pointless quibbling to how players have to word their readied actions.

And creating a specified difference between "begins to cast a spell" and "cast a spell" doesn't? This thread is evidence that it does. Your creative choice of wording shouldn't have an impact on the fiction beyond what a player would have if they shared the same intent but didn't choose that same wording.

You're just trading your example here for an equally infuriating one "No, you don't get to attack first as you intended. Not because the rules say so, but because you didn't word your trigger specifically enough. Tim did, however, so go ahead and take that reaction."

People are going to fight about it. People are fighting about it here.