Does blocking an attack with the Shield spell still trigger Armor of Agathys?

Question

I am contemplating a Oath of Conquest Paladin / Sorcerer multiclass character, with a 1 level dip in hexblade warlock.

This character will have access to the Armor of Agathys and Shield spells, which potentially allows for a pretty nice combo.

The Shield spell states (PHB 275):

Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell...

Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack,

It looks like you are indeed hit by an attack, but since you have a bonus to AC, you can potentially force that attack to miss instead.

Armor of Agathys states (PHB 215),

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

If I cast Shield and cause an attack that "hit" me to miss, does Armor of Agathys still deal damage?

I am leaning toward yes, though this combo seems a little too strong--Shield is already a strong spell, and this character will eventually have 9 1st level spell slots and a 7th level spell slot. Not only can they freely block attacks with Shield, but they can also deal up to 35 (5d10) damage to the attacker without an attack roll or saving throw. While a Warlock would have to spend both of their spell slots to do this once, my character would be able to do this 4 times with spell slots to spare.

Some notes:

• Related questions ask about reducing the damage from a confirmed hit to zero. This question is asking about what happens when the Shield spell causes the attack to miss entirely.
• A number of online resources, such as the Roll20 5th edition compendium, seem to be missing the correct casting time for the Shield spell. Answerers should make sure they're looking at the correct version from the PHB.

Answer 1

No, armor of Agathys would not do its damage.

Shield is one of the few reaction spells that 'interrupts'/potentially cancels its trigger, as clarified by the DMG in the 'Adjudicating Reaction Timing' section:

For example, the opportunity attack and the shield spell are clear about the fact that they can interrupt their triggers.

(See also: @Rubiksmoose's answer to 'Do reactions interrupt their triggers or not?')

Since it 'interrupts' the hit and changes it to a miss, there is no longer a hit to trigger armor of Agathys's damage effect; 'interrupt' implies shield affects/changes the trigger during the triggering event and prevents it from occurring, and there's no longer a hit for the armor of Agathys to trigger off of.

Jeremy Crawford, lead rules designer of D&D5e, unofficially indicates this is the logic to follow as well in a response to a question about 'on hit' riders interacting with shield:

@mikemearls @JeremyECrawford If an Open Hand Monk hits a creature with the shield spell prepared and uses it's Open Hand Technique feature to stop it from using reactions until the end of the Monk's next turn, would the creature be able to cast shield to cancel the attack?

[@MrNubcakz, 1:34 PM - 30 May 2018]

Shield spell—its description says it works against the triggering attack, which means it can cause that attack to miss. If the attack has a special effect that relies on it hitting, that effect doesn't occur if the attack is turned into a miss. #DnD

[@JeremyECrawford, 4:00 PM - 30 May 2018]

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For an analogy, let's use another example of an interrupting reaction that's a bit more clear cut: the opportunity attack. Lets look at the timing of that trigger:

You can make an opportunity attack when a hostile creature that you can see moves out of your reach.

Basic Rules

So the attack's trigger is when they move out of reach, but interrupts that movement and occurs before they've actually moved out of reach.

Let's imagine a scenario where an enemy is between a fighter and a field of spike growth, each of which are 5 feet from the enemy. The enemy runs directly away from the fighter into the spike growth field, both leaving the fighter's reach and moving into the area of spike growth at the same time.

Normally, the enemy would immediately take the 2d4 damage from the spike growth. However, the fighter decides to take an opportunity attack, hitting the enemy and knocking it out with a nonlethal attack. The enemy is now stopped exactly where it started, within 5 feet of the fighter. We would not expect it to take spike growth damage, as the enemy's movement away from the fighter/into the area of spike growth never actually happened- it was interrupted and stopped, as evidenced by the enemy remaining within its square.

To me, this same logic applies to how shield interacts with the hit it interrupts- it has no longer happened, so nothing else can trigger off of it.

Answer 2

Wow, good combination.

Wording is important here. Armor of Agathys lasts for an hour without concentrating, so you can definitely have it active while simultaneously using shield. According to that AoA,

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

It doesn't say that the attack that provokes the spell must deal damage, and there is no reaction time; the cold damage is triggered by the act of hitting the caster, and occurs instantly. Also triggered- your ability to cast shield.

Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell

In order to cast shield, you have to be hit by the attack first... and if you're hit and you have those temp hit points, the attacker takes damage. If we're just going off the spell descriptions, then for the cost of two first level slots you can have a snazzy variant of a fire shield.

Shield is a bit of a paradox, however, so it helps to think of the intent of the spell. It boils down to how you're supposed to interpret the fact that shield also applies to the attack that triggered it. The spell description gives no guidance, so you could easily rule that the spell blocks the hit from ever occurring, as you mention- but if so, then the spell couldn't have been triggered by that attack, since you weren't hit. My interpretation is that your increased AC from the spell is meant to demonstrate the spell absorbing, not deflecting, the effects of the attack, just as it absorbs the effects of a magic missile- if the attack can beat your new AC, then it is smashing through your magical last line of defense. In this case, too, the two spells should be able to stack, since the hit still occurs if you're protected by shield, it's just kept from hurting you. This interpretation is arguable, I'll grant, as it's implying that a first level spell can absorb any level of damage and AC increase implies avoiding a blow rather than enduring one, but it avoids the issue of the trigger paradox and shield is a very short-term defense compared to the more powerful abjurations.

Bottom line- the two spells share a trigger, and as long as they do, both spells can apply to the same attack.

Answer 3

By strict RAW, yes, although I agree this is most definitely not RAI.

Let's approach this logically. A shield doesn't give you a +2 bonus to AC because it helps you dodge attacks better. It helps you block them, that's the entire purpose of it being large and attached to your arm in front of your body. By a strict RAW reading, Armor of Agathys should trigger anytime the last 2 AC of your armor gets rolled on the attack.

Also by strict RAW, plate mail is not exactly what one would call the most dexterous of armors (what with it's whopping + 0 from DEX). So any roll including the 8 from plate mail should also trigger Armor of Agathys.

That leaves your base 10 AC to be the only portion that qualifies as your standard reflexes, plus whatever DEX you were able to add (if you're in armor that lets you) as your dodge bonus.

Now, LOGICALLY this is sound, and the wording of the spell is such that damage is NOT a requirement, a mere hit is.

So here's where we get into the problem. What qualifies as a hit? If I punch a target and beat their AC, I hit them right? What if my STR mod is -1? I do 0 damage, but I still hit. Do I get affected by Armor of Agathys? After all, I met the criteria, I struck my target, I beat it's AC, so by any measure, I successfully hit and the spell should trigger. The spell says it should, and I agree. Whether you did damage with your attack is irrelevant to what triggers the spell.

This is actually supported in Mike Mearls' Sage Advice tweet with respect to Ray of Frost:

If a creature is immune to cold and is hit by "Ray of Frost" do they suffer the 10-foot speed penalty in #DnD 5E?

Yes - immunity applies only to damage.

This means that a target qualifies as being hit when they are physically or magically touched by the attack in question, irrespective of whether or not they take damage. This "touch" is reflected by beating their AC.

So, with that being said, I have to say that this is a solid yes, but probably not what they intended with the spell.

This confirmation from Crawford addresses that the intent is that the attack becomes a miss. In that cast, and confirming the RAI, Armor of Agathys would NOT trigger.

Answer 4

No, the damage from Armor of Agathys wouldn't be triggered.

Jeremy Crawford, lead rules designer for D&D, addresses a similar question on Twitter here:

If an Open Hand Monk hits a creature with the shield spell prepared and uses it's Open Hand Technique feature to stop it from using reactions until the end of the Monk's next turn, would the creature be able to cast shield to cancel the attack?

Shield spell—its description says it works against the triggering attack, which means it can cause that attack to miss. If the attack has a special effect that relies on it hitting, that effect doesn't occur if the attack is turned into a miss.

As such, given the above clarification, it seems logical to include that Armor of Agathys would not trigger if Shield turned the hit into a miss. If the target of an attack casts Shield and turns the hit into a miss, then it's as if the hit never happened; nothing that would have applied on a hit is able to apply after Shield causes the attack to miss.

Normally, the sequence is as follows: (1) attack roll is made (2) attack hits or misses (3) damage and other effects of the hit are applied.

However, Shield interrupts this sequence and takes place after step 2. Due to the way the spell works, it can turn a hit into a miss, so even though it happens after step 2, it can actually retroactively change the outcome of step 2 itself. As a result, if Shield turns a hit into a miss, any effects that would have applied on the hit can no longer apply after Shield makes it miss.

Answer 5

Yes

Armor of Agathys' trigger:

If a creature hits you with a melee attack while you have these hit points(...)

Shield trigger:

1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell.

Let's look at this mechanically, step by step.

Step 0: You have Armor of Agathys cast on yourself, and one ready 1st level spell slot to cast Shield with.

Step 1: Somebody targets you with a melee attack, and hits. At this point, your character is hit by the attack. This is the point at which you choose to cast Shield, and also the trigger point for the damaging effect of Armor of Agathys. However, Shield takes a reaction to cast, and going by the rules of the Ready action: (reaction-time spells themselves say only that they "(...) are cast in response to some event.")

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

Since Armor of Agathys doesn't take a reaction to take effect, it would activate before you can take your reaction, since it basically happens at the same time as you "being hit". So...

Step 2. Armor of Agathys deals it's damage, and then you can take your reaction to cast Shield, which (possibly) changes the state of the attack from "hit" to "missed", causing you or your AoA to take no damage or other ill effect.