I have found this Q/A ("Does damage from Armor of Agathys take place before or after a character takes damage from an attack that hits?") and also this Q/A ("What happens if a creature is killed between its attack and damage rolls") both of which use the idea that getting hit by an attack and taking damage from an attack happen at different times.

The armor of Agathys spell is an example of when this doesn't matter as it states:

If a creature hits you with a melee attack while you have these hit points, the creature takes 5 cold damage.

This effect does not require any sort of reaction, it simply happens simultaneously with the hit.

However there are features where the answer does matter such as the Sun Soul Monk's Sun Shield which states:

If a creature hits you with a melee attack while this light shines, you can use your reaction to deal radiant damage to the creature.

This requires your reaction, and we know that reactions (typically) happen after their triggers as supported by this Q/A ("Do reactions interrupt their triggers or not?") so the Sun Shield effect definitely happens after you are hit (making it a distinct scenario from armor of Agathys).

But are getting hit and taking damage simultaneous events?
If yes, then the reaction would occur after the hit and thus after the damage.
If no, then the reaction would occur after the hit but before the damage.

When the reaction can occur is important.
Let the Monk have only 1 HP left and be hit by an attack from a creature.
If they are hit and take damage simultaneously, then they would fall unconscious and be unable to take the reaction.
If the hit happened before the damage they could take their reaction, dealing damage to the attacking creature, and then take the damage, falling unconscious as a result.



Being hit and taking damage are part of the single “event” Resolve the Attack which says:

3. Resolve the attack. You make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.

Getting hit and taking damage are different triggers that reactions or other game effects can be hung off because it’s possible to be hit and not take damage e.g. if you are immune to the damage type or the attack has a non damaging effect. Similarly it’s possible to take damage without being hit e.g. by an effect that isn’t an attack.

If the being hit allows a reaction, it can be taken after you take damage - provided you are still capable of taking actions (reactions are actions). If the attack incapacitates you, you cannot take the reaction.

  • \$\begingroup\$ Q2’s accepted answer makes the giving and receiving of damage seem simultaneous, which I’m not sure is right, but Crawford apparently supports the A to Q1 \$\endgroup\$ – D. Ben Knoble Aug 16 at 1:14
  • \$\begingroup\$ @DaleM I've removed my comment (as I've provided my own answer now) and suggest you do the same \$\endgroup\$ – Medix2 Aug 16 at 15:31
  • \$\begingroup\$ Keep in mind that some reactions can retroactively cancel the hit, such as the Shield spell, which increases your AC after a hit, and that new AC can prevent you from having been hit in the first place. \$\endgroup\$ – PotatoEngineer Aug 16 at 16:01
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    \$\begingroup\$ @Blits The Shield spell is an odd one and involves a time paradox. It works because magic. \$\endgroup\$ – Dale M Aug 16 at 20:45
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    \$\begingroup\$ @Blits I so wish reactions which reduce damage after you've taken damage and reactions which can prevent hits after you've been hit had a more explicit explanation on when they are happening. There are non-magic features that can turn hits into misses such as the Cavalier Fighter's Warding Meneuver. And non-magic features that reduce damage you take after you've taken it such as the Horizon Walker's Ranger's Spectral Defense feature or the Ancestral Guardian Barbarian's Spirit Shield \$\endgroup\$ – Medix2 Aug 17 at 13:05

The sentence structure for Armor of Agathys uses 'hits', present tense, indicating that the two actions (you taking damage and the opponent taking damage) happen simultaneously. A reaction, according to the PHB:

A reaction is an instant response to a trigger

Except Xanathar's has this to say, which is:

If you’re unsure when a reaction occurs in relation to its trigger, here’s the rule: the reaction happens after its trigger completes, unless the description of the reaction explicitly says otherwise.

Let's say, for instance, a kobold (5 hit points) decided to wail on your Armor of Agathys using wizard. The kobold hits, rolls low, and deals three damage. The Armor of Agathys activates and kills the kobold. Even if that happened before you rolled damage, that happened after you got hit, and the general rule is that whenever you get hit, you take damage. There's no specific rule for when you can kill someone who hits you with a weapon attack that it negates the damage dealt by the attack.

Now let's take a look at the Monk case you presented. According to the two reactions rules, the reaction takes place as soon as the trigger finishes, however that's when the reaction occurs. You can take the reaction once the trigger occurs. Since the trigger is 'getting hit with an attack', and 'getting hit' is part of the overall 'attack' action, the damage occurs simultaneous to the trigger, whereas your reaction occurs after that. However, since the reaction is stated to be 'an instant response' to the trigger, the reaction can be taken, but it happens after the trigger, as the language is 'reaction happens' in Xanathar's. Note that it says 'happens', not 'take the reaction action', which means that the reaction action is triggered simultaneous to the trigger, but it only occurs after the trigger. A bit nonsensical, yes, but I don't write the rules, I just read as written.

So, to summarize, you can trigger the reaction, however, it only activates after damage, at which point you are at 0 hit points, go unconscious, but there's no rule against your unconscious body dealing damage when you already took an action while conscious. It's really no different than jumping off a building, taking damage, and then having your unconscious body fall on an enemy, from a mechanics standpoint, at least.

Final conclusion? Your unconscious Monk body deals damage thanks to a choice you made while you were still conscious.

  • \$\begingroup\$ I explained my logic a bit more. You aren't taking the reaction while unconscious, the reaction is occurring while you're unconscious. 'Damage occurs simultaneous to the trigger' means that getting hit and taking damage are simultaneous events, as they're both part the 'Attack' action. \$\endgroup\$ – Halfthawed Aug 15 at 22:36
  • \$\begingroup\$ Neither answer given is inconsistent with my answer. \$\endgroup\$ – Halfthawed Aug 15 at 23:06
  • \$\begingroup\$ One says there is a time between the hit and the damage and the other says: "lastly, damage is rolled and then applied." \$\endgroup\$ – Medix2 Aug 15 at 23:15
  • \$\begingroup\$ I agree with the conclusion of the first answer, and the second answer is only saying that in relative terms to when you roll damage, not when the game determines you roll. In either event, I have no problem arguing with them, as neither quotes a definitive source and just reads the rulebook. \$\endgroup\$ – Halfthawed Aug 15 at 23:18

Damage and hits likely happen mechanically at the same time

Note that I do agree with the answer from @DaleM and am just providing this as some interesting information.

The lead rules designer, Jeremy Crawford, has made a couple tweet regarding attacks hitting and damage, in particular this one and this one

Q. Solar HITS w/ Slaying LB on a 101~HP target, Death con saving throw req. start with the HIT or after damage reduction?
A. Slaying Longbow sequence:
1. Hit
2. Deal damage (apply any resistance)
3. Make saving throw if the target has hit points ≤ 100

Q. Just for clarification, this means you can declare a divine smite/sneak attack after an attack roll, but before a dmg roll?
A. (1) You make an attack roll.
(2) You hit or miss.
(3) You roll damage if you hit. "When you hit" happens at number 2.

Both of these state that damage happens as a consequence of hitting a creature but whether the damage happens after the hit is unclear.
In the second quote we also cannot tell if the explanation is about the mechanics of the game or how it plays out in real-time. (just because we roll damage dice second doesn't mean it mechanically happens second).

In fact, there is a section in the DMG on "Rolling Attacks and Damage" which states:

Players are accustomed to rolling an attack roll first and then a damage roll. If players make attack rolls and damage rolls at the same time, the action moves a little faster around the table...

Changing the way in which you roll should not change the way in which hits and damage mechanically occur. This further supports the idea that the damage dice being rolled second has no impact on whether damage happens second.

One slight issue with having the two be simultaneous events is this rule from Xanathar's Guide to Everything:

If two or more things happen at the same time on a character or monster's turn, the person at the game table-whether player or DM-who controls that creature decides the order in which those things happen. For example, if two effects occur at the end of a player character's turn, the player decides which of the two effects happens first.

Clearly this would be a bad rule to apply as it would allow damage to occur before the hit. Luckily for us, the rules in Xanathar's are optional.

There is also a section of the rules on "Making an Attack" which states:

3. Resolve the attack. You make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.

Whether "On a hit" is mechanically at the same time as the hit or not is not something we can glean from the rules. It could be interpreted to mean the damage happens only if you hit, but at the same time or that damage happens after you hit (which requires you to hit in the first place).

In the end it is unclear whether damage mechanically happens after you are hit.

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    \$\begingroup\$ I suggest using this phrasing (up to you) damage happens after you hit a creature is better presented as damage happens as a consequence of hitting a creature which renders the point of before and after moot. Before and after looks to me to be a red herring. Your answer, use if you like or don't if you don't. \$\endgroup\$ – KorvinStarmast Aug 16 at 15:38
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    \$\begingroup\$ Xanathar's is an optional rule for helping people get past "what do I do now?" points. It isn't a replacement rule for what is in the core books. I honestly agree that it makes no sense (at all) from a personal PoV: the DM making a ruling as needed is what the core game calls for. It seems to have been offered to people who simply can't embrace that means of keeping play moving. \$\endgroup\$ – KorvinStarmast Aug 16 at 15:42
  • \$\begingroup\$ No, my failure in clarity there. The suggestion was damage happens as a consequence of hitting a creature as a replacement to damage happens after you hit a creature and if that does not fit the answer, then flush it. :) \$\endgroup\$ – KorvinStarmast Aug 16 at 15:49
  • \$\begingroup\$ @KorvinStarmast I've edited my answer a good bit and included your ideas \$\endgroup\$ – Medix2 Aug 16 at 15:57

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