D&D 5E Reactions

[Ovinomancer]

From the combat rules: "You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach."

You can call this "before the trigger" or "interrupting the trigger," whichever. The difference is purely semantic, but "before the trigger" is how it's phrased in the rules. "Before the trigger takes effect" might be a more precise way of phrasing it.

This is why M:tG invented the stack. It might be going a little far to explicitly write the stack into the D&D rules, but IMO a stack-like approach is the right way to think about these things. First the trigger goes on the stack; then your reaction goes on the stack; then your reaction resolves; then the trigger resolves.

Okay, then, please answer the question: when can you make an opportunity attack? The answer is, "when a hostile creature that you can see moves out of your reach." They must do this before you can make an opportunity attack. How does that attack resolve? Well, it interrupts and occurs immediately before that creature leaves your reach. You cannot make an OA until and unless a hostile creature you can see leaves your reach.

 

[Dausuul]

Okay, then, please answer the question: when can you make an opportunity attack? The answer is, "when a hostile creature that you can see moves out of your reach." They must do this before you can make an opportunity attack. How does that attack resolve? Well, it interrupts and occurs immediately before that creature leaves your reach. You cannot make an OA until and unless a hostile creature you can see leaves your reach.

Like I said, it's a semantic difference. "Before" is just what the rulebook says; clearly the OA cannot happen until a creature attempts to leave your reach, and equally clearly it must happen before the creature actually does leave your reach. That's why I like to think of it in terms of the M:tG stack, which draws a distinction between an event being initiated (put on the stack) and the same event taking effect (resolving).

My point is that there is no blanket rule saying reactions happen after the trigger. That is a rule specific to readied actions, which are one particular type of reaction.

 

[spectacle]

Okay, then, please answer the question: when can you make an opportunity attack? The answer is, "when a hostile creature that you can see moves out of your reach." They must do this before you can make an opportunity attack. How does that attack resolve? Well, it interrupts and occurs immediately before that creature leaves your reach. You cannot make an OA until and unless a hostile creature you can see leaves your reach.

How can you interrupt something that's already happened? A creature is either inside your reach or not, and if it is outside you can't hit it. So the opportunity attack must happen before the creature leaves your reach or it would always miss.

Alternatively you have to accept that timing in the D&D rules don't nescessarily correspons 100% with what is happening in the story.

 

[procproc]

You don't cast shield...because shield is a reaction...and you don't have a reaction when hit by SG...or a ghoul [if you fail your save]. I really don't understand what you're not following.

...

If you are shocking grasped/electrocuted or paralyzed by a ghoul...what you "want" to do is completely irrelevant. Again, I don't understand what you're not getting here...if you have no reaction, in these specific, really rather limited, circumstances in the big picture of the game as a whole, then you can't take a reaction.

...

Where is the disconnect here?

I will say and do think, if nothing else, this thread has proven once and for all that WotC REALLY screwed the pooch entitling this sometimes-first/sometimes-after/only-when-a-trigger-happens-moment-in-combat as a "Reaction."

The disconnect is that without a clear structure for how the timing of reactions works with regard to being hit/taking damage, you end up with a teeming underbelly of weird, unintuitive interactions that aren't necessarily consistent with each other. So far, we've got SG, attacks that knock you unconscious, attacks that paralyze /petrify/incapacitate, and attackers with the Mage Slayer feat vs. any number of reactions that trigger on being hit or damaged, including Shield, UC, and Hellish Rebuke.

So if, for example, the implication of having these work consistently is that Uncanny Dodge can't be used on an attack that would knock you unconscious, that's a huge nonintuitive interaction that should've been called out in the description of UC. And honestly, granting an ability that a player can only use when something bad happens to them is fine, but then telling them they can't use it because of a corner-case unintuitive rules interaction that comes up not-infrequently in unpredictable situations is pretty much a recipe for making a player unhappy.

And yeah: "rulings, not rules", and a DM can certainly apply the "players win ties" philosophy mentioned earlier in the thread. But rules that are so vague as to encourage these kind of situations are *not* good rules.

 

[Ovinomancer]

Like I said, it's a semantic difference. "Before" is just what the rulebook says; clearly the OA cannot happen until a creature attempts to leave your reach, and equally clearly it must happen before the creature actually does leave your reach. That's why I like to think of it in terms of the M:tG stack, which draws a distinction between an event being initiated (put on the stack) and the same event taking effect (resolving).

My point is that there is no blanket rule saying reactions happen after the trigger. That is a rule specific to readied actions, which are one particular type of reaction.

I think that a large part of this discussion hinges on people assuming M:tG stack mechanics when they don't exist in D&D. There is no stack or established general order of resolution. OAs are called out specifically in the DMG as reactions with specific timings, in OAs case, as something that can interrupt it's trigger. The general rule (also in the DMG) is that reactions occur after their triggers are completed.

How can you interrupt something that's already happened? A creature is either inside your reach or not, and if it is outside you can't hit it. So the opportunity attack must happen before the creature leaves your reach or it would always miss.

Alternatively you have to accept that timing in the D&D rules don't nescessarily correspons 100% with what is happening in the story.

You cannot take an OA reaction until a hostile creature you can see moves out of your reach. Literally can't. When you're allowed to take an OA, the hostile creature that you can see has moved out of your reach, but the OA reaction allows you to rewind a moment and interrupt that leaving before it completes. The timing is -- trigger occurs -> reaction occurs. In every case. Sometimes, like with shield and OAs, the reaction is allowed to timewarp and affect the trigger, possibly invalidating their own trigger. However, according to the DMG, if that isn't specifically called out by the reaction, then the reaction occurs after it's trigger.

To point, Uncanny Dodge has 'being hit' as it's trigger. That must occur and resolve before UD acts. A hit applies the effects of the hit, usually damage, sometimes damage + other, sometimes just other, and then the UD kicks in. The specific wording of UD says that it halves the damage from the attack. That damage is already there, UD just counters some of it retroactively because that's what it says it can do. There's no stack, where UD goes on right after 'hit' but before 'effects' because there's no there there. The hit occurs, then UD goes and modifies the results of the hit. In the case of shocking grasp, nothing UD can do can remove the 'can't react' so you can't react with UD. That part's done already before you can use UD. In a modification of my previous, you can use shield against shocking grasp because it interrupts it's trigger which means it interrupts the application of 'can't react.' This creates the occasion of paradox, but it's not world ending.

 

[Ovinomancer]

The disconnect is that without a clear structure for how the timing of reactions works with regard to being hit/taking damage, you end up with a teeming underbelly of weird, unintuitive interactions that aren't necessarily consistent with each other. So far, we've got SG, attacks that knock you unconscious, attacks that paralyze /petrify/incapacitate, and attackers with the Mage Slayer feat vs. any number of reactions that trigger on being hit or damaged, including Shield, UC, and Hellish Rebuke.

So if, for example, the implication of having these work consistently is that Uncanny Dodge can't be used on an attack that would knock you unconscious, that's a huge nonintuitive interaction that should've been called out in the description of UC. And honestly, granting an ability that a player can only use when something bad happens to them is fine, but then telling them they can't use it because of a corner-case unintuitive rules interaction that comes up not-infrequently in unpredictable situations is pretty much a recipe for making a player unhappy.

And yeah: "rulings, not rules", and a DM can certainly apply the "players win ties" philosophy mentioned earlier in the thread. But rules that are so vague as to encourage these kind of situations are *not* good rules.

Not really. Being knocked unconscious is an effect of taking damage. UD reacts to being hit, so it occurs before and modifies the incoming damage before you check for being unconscious. Ghoul paralysis can go either way, depending on how you want to rule the save mechanic - the attack applies the save mechanic, but the failed save applies the paralysis. You can lump those together or not however you want the deadliness of ghouls to be (personally, I like nasty ghouls).

 

[ProphetSword]

I think people need to come to the understanding that D&D no longer has rules for every situation like it did in the 3.5 era. Honestly, we got along fine without it during the days of Basic/AD&D, and can do so again if people stop expecting the game to have rules like a board game.

The correct answer is always whatever your DM rules. If you don't trust your DM, find another one or play a different edition. Making up rules or importing them from card games will not get you an official answer. You will be at the mercy of the DM no matter what conclusions anyone makes here, or if you are the DM you will need to rule it yourself.

 

[Cognomen's Cassowary]

I think that a large part of this discussion hinges on people assuming M:tG stack mechanics when they don't exist in D&D.

I think a large part of it is people assuming the only reaction which interrupts is "an interrupt" in M:tG terms. Any reaction which breaks the normal flow of an act interrupts (by the dictionary definition), be that act attack, movement, or urinating and falling into a fetal position. That is what that section of the DMG is about: whether or not a reaction interrupts is a function of its timing, not of an explicit "interrupt" aspect or effect of the reaction.

UD reacts to being hit, so it occurs before and modifies the incoming damage before you check for being unconscious.

Right. If the normal flow of the attack is this:
declare attack > roll to hit > check for attack success > roll damage > apply damage and other effects > check for unconsciousness

Then uncanny dodge changes it to this:
declare attack > roll to hit > check for attack success | interruption if attack is successful: halve incoming damage | > roll damage > apply damage and other effects > check for unconsciousness

What procproc is saying--and I agree--is that whether the condition which would prevent uncanny dodge is blindness, unconsciousness, or shocking grasp's effect, it is applied after the reaction has been triggered and taken effect.

What you and others have been implying (and please correct me if I'm wrong) is a flow that looks more like this:
declare attack > roll to hit > check for attack success > apply other effects > roll damage > apply damage

where
declare attack > roll to hit > check for attack success | uncanny dodge is triggered here | > apply other effects > roll damage | but doesn't occur until here, if it can | > apply damage

The division of the effects of an attack such that some are applied ahead of others is not supported by the rules, and the idea that a reaction can be triggered but then not occur if it is retroactively made unusable is similarly unsupported. Both are counter-intuitive complications introduced to make this particular interaction work the way it seems you think it should. Jeremy Crawford's ruling, as I see it, is a stealth erratum which changes the trigger of uncanny dodge to "when you take damage from an attack."

But yes, as ProphetSword says, the game doesn't need page upon page of minor rules tweaks and clarifications. I'll play this situation, should it ever come up, however my DM says.

 

[Hriston]

Okay fine...a brgthrra monster....horrible horrible beast with tentacles and slobbering...ugh...I shoots blinding rays that do damage and blind the traget on a hit. Can the rogue use UD? Even if the blindness effect allows a save by your logic the rogue cant use UD because he can't see the brggthra beast...

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Yes, he can. Assuming the Brggthra Beast is an attacker he can see, the Rogue is able to use Uncanny Dodge. IMO, that's the spirit of Uncanny Dodge. As long as you can see your attacker at the moment of the attack, it doesn't matter that you are blinded subsequently. There's nothing about being hit by the Beast's attack, as far as I can tell, that explicitly denies use of reactions.

 

[Greenstone.Walker]

Okay, then, please answer the question: when can you make an opportunity attack? The answer is, "when a hostile creature that you can see moves out of your reach."

I think you are wrong there.

The answer is "When a hostile creature that you can see attempts to move out of your reach."

The attack occurs right before the creatures leaves your reach. The result of the attack might mean the creature is prevented from actually moving out of your reach (perhaps it is dead, perhaps you had Sentinel feat).