Booming Blade and Opportunity Attacks

[ATHATH]

Suppose I hit John with the Booming Blade cantrip. On his turn, he tries to move out of my reach.

1. Does he proc Booming Blade's second damage tick before or after I get my opportunity attack?
2. If the answer to 1. is "after" and I have War Caster, if I replace my War Caster opportunity attack with a another casting of Booming Blade, will I lose out on the second damage tick from this second casting (or maybe the first casting's?), as John is technically still under the effects/duration of the first casting?
3. Can John proc an opportunity attack from me without proc'ing the second damage tick of Booming Blade by declaring intent to step 5 ft. backwards, taking my opportunity attack, and then deciding not to follow through on his movement?

[JNAProductions]

1) Booming Blade would trigger after your AoO, since if it triggered before, they'd be out of range.

2) It was after, so you'd only get one trigger of Booming Blade.

3) My ruling would be (following up on the above) that they'd trigger Booming Blade, since they're already under its effects when they move, and would have to willingly move to provoke anyway. So either they're taking it and an AoO (which could be a Booming Blade, but would still only do the movement damage once) or they'd stand still and not take anything.

[PhoenixPhyre]

1) Booming Blade would trigger after your AoO, since if it triggered before, they'd be out of range.

2) It was after, so you'd only get one trigger of Booming Blade.

3) My ruling would be (following up on the above) that they'd trigger Booming Blade, since they're already under its effects when they move, and would have to willingly move to provoke anyway. So either they're taking it and an AoO (which could be a Booming Blade, but would still only do the movement damage once) or they'd stand still and not take anything.

I concur with this.

On 3) I'm very not fond of mechanical-metagaming, so the behavior here is kinda hinky. You don't declare a move, you move. And once you've done so, you can't take it back. You can't say "oh, I'm going to step back" and then, when hit with an OA, not step back. Unless, of course, Sentinel. Or dead. By the time the OA (assuming it doesn't down you or immobilize you) completes, so has that 5' of movement.

[Greywander]

On 3) I'm very not fond of mechanical-metagaming, so the behavior here is kinda hinky. You don't declare a move, you move. And once you've done so, you can't take it back. You can't say "oh, I'm going to step back" and then, when hit with an OA, not step back. Unless, of course, Sentinel. Or dead. By the time the OA (assuming it doesn't down you or immobilize you) completes, so has that 5' of movement.
My interpretation is that the enemy would begin their move, which is then interrupted by the OA. The OA happens before any movement has actually occurred, as otherwise they would be out of range. After the OA has concluded, the enemy is still in their original location and can decide whether or not they still want to move. Usually there won't be a reason not to go ahead and move, but in the case of Booming Blade they might decide not to move after all to avoid the secondary damage.

[PhoenixPhyre]

My interpretation is that the enemy would begin their move, which is then interrupted by the OA. The OA happens before any movement has actually occurred, as otherwise they would be out of range. After the OA has concluded, the enemy is still in their original location and can decide whether or not they still want to move. Usually there won't be a reason not to go ahead and move, but in the case of Booming Blade they might decide not to move after all to avoid the secondary damage.

I don't agree. They've begun their move, but haven't completed it. But in order for the OA to even proc, they have to be in the process of moving out of reach. Which, for my purposes, means they have to finish that segment of motion. And doing that is already trigger enough for BB. In fact, I'd say that "has triggered OA by starting to move === has triggered BB's damage." They're separate things that have the same trigger, so they resolve simultaneously.

Yes, the OA resolves before the motion finishes. But not after it starts, which is enough to trigger BB.

[Arkhios]

Since movement is not an action in this edition, one can split their movement within their turn however they please. Even stop moving immediately after they're hit by Booming Blade (assuming they know what it does, which is an entirely different question whether they should know).

Therefore, my interpretation is this:

As long as you actually can cast Booming Blade in place of an Opportunity Attack (e.g. you have War Caster feat), you can by RAW cast it against someone whose movement provoked an Opportunity Attack.

The Booming Blade hit takes place after the movement is finished up to the point that triggered the Opportunity Attack. The target may choose to stop moving beyond that, avoiding the extra damage from Booming Blade (although, as a house rule I would ask for a skill check or something to recognise the spell and/or effect it bestows, before they can decide whether they move more or stop moving, but I realize this is not RAW).

[PhoenixPhyre]

Since movement is not an action in this edition, one can split their movement within their turn however they please. Even stop moving immediately after they're hit by Booming Blade (assuming they know what it does, which is an entirely different question whether they should know).

Therefore, my interpretation is this:

As long as you actually can cast Booming Blade in place of an Opportunity Attack (e.g. you have War Caster feat), you can by RAW cast it against someone whose movement provoked an Opportunity Attack.

The Booming Blade hit takes place after the movement is finished up to the point that triggered the Opportunity Attack. The target may choose to stop moving beyond that, avoiding the extra damage from Booming Blade (although, as a house rule I would ask for a skill check or something to recognise the spell and/or effect it bestows, before they can decide whether they move more or stop moving, but I realize this is not RAW).
Bb is triggered by movement. OA is triggered by movement out of reach. OA's trigger is included with BB's trigger unless you believe the world is snapped to a 5' grid, and even then it makes little sense to say that you can move enough to trigger OA without actually moving at all (to avoid triggering BB)

[Reach Weapon]

[...] then becomes sheathed in booming energy until the start of your next turn. If the target willingly moves 5 feet or more before then, the target takes 1d8 thunder damage, and the spell ends.

Because it triggers on a willing movement of 5' or more, when it's cast as part of an Opportunity Attack (which happens during that movement), I believe the decision point against triggering the effect happens in the square just outside the reach of the caster. Put another way, a target that would never choose to trigger Booming Blade, would nonetheless be out of the reach of the caster when it stopped.

T_C - End Result: Target, non-longer occupied 5' square, Caster

It wouldn't matter if the target was already sheathed in booming energy, as the different trigger points for the damage would keep the effects separate (not stacked).


You don't declare a move, you move. And once you've done so, you can't take it back.

I'm not sure we're quite disagreeing, but I do think that there is a moment between announcing character predicable consequences and when the player has taken their hand off the chess piece, as it were.

That said, playing on a grid does mean that there is no place where a character could trigger an Opportunity Attack without triggering an existing Booming Blade effect, but also that one would need additional movement to trigger a new one.

[Talamare]

Suppose I hit John with the Booming Blade cantrip. On his turn, he tries to move out of my reach.

1. Does he proc Booming Blade's second damage tick before or after I get my opportunity attack?
2. If the answer to 1. is "after" and I have War Caster, if I replace my War Caster opportunity attack with a another casting of Booming Blade, will I lose out on the second damage tick from this second casting (or maybe the first casting's?), as John is technically still under the effects/duration of the first casting?
3. Can John proc an opportunity attack from me without proc'ing the second damage tick of Booming Blade by declaring intent to step 5 ft. backwards, taking my opportunity attack, and then deciding not to follow through on his movement?

1 - After your AOO, but to be clear... They may choose to STOP MOVING after you hit with Booming Blade, thus not triggering it. They would remain where they started.

2 - They are currently affected by Booming Blade, They start moving, AOO Triggers, Booming Blade can't stack so it doesn't matter if you hit or not. They are still allowed to stop moving at this point to not trigger Booming Blade (In which case you were allowed essentially a free AOO)

3 - Oh man, I answered 3 by accident...

Edit2- 4 - I know it wasn't asked but it's usually a problem with this spell... and of course if they were forced or compelled to move by any magical means or spell; Booming Blade doesn't trigger... but you might still get an AOO depending on what it was.

Edit -
Note, I'm not arguing what I believe is correct.

I'm telling you what Sage Advice has ruled as correct.
https://www.sageadvice.eu/war-caster-hitting-with-booming-blade/

[Chronos]

The PHB does actually have a rule for how to resolve effects that would otherwise be simultaneous: The creature whose turn it is decides in what order they're resolved.

[Reach Weapon]

I'm telling you what Sage Advice has ruled as correct.
https://www.sageadvice.eu/war-caster-hitting-with-booming-blade/

You might want to clarify all this further, as it appears there are several assertions in your post not covered by that to which you linked (or other Sage Advice I recall at the moment).

[Arkhios]

Bb is triggered by movement. OA is triggered by movement out of reach. OA's trigger is included with BB's trigger unless you believe the world is snapped to a 5' grid, and even then it makes little sense to say that you can move enough to trigger OA without actually moving at all (to avoid triggering BB)

OA triggers as soon as the target moves away from your reach (farther than 5 ft). By then, they're already in the next 5ft. window, whether or not they choose to move further. But that's besides the point. It doesn't matter how far beyond they moved. What matters is that the BB does not trigger from the same movement that already triggered OA, UNLESS THE TARGET CONTINUES THEIR MOVEMENT AFTER BEING HIT BY BB. You resolve the attack roll to hit with BB first, and only after that the rider effect of the spell itself. But the target can choose not to move an inch further after being hit (whether or not we're using a 5' grid).

You're willfully ignoring what I said. Stop that.

[PhoenixPhyre]

OA triggers as soon as the target moves away from your reach (farther than 5 ft). But that's besides the point. It doesn't matter how far beyond they moved. What matters is that the BB does not trigger from the same movement that already triggered OA, UNLESS THE TARGET CONTINUES THEIR MOVEMENT AFTER BEING HIT BY BB. You resolve the attack roll to hit with BB first, and only after that the rider effect of the spell itself. But the target can choose not to move an inch further after being hit (whether or not we're using a 5' grid).

You're willfully ignoring what I said. Stop that.

Maybe I misunderstood? I was under the impression that the case at hand was
1 Target within reach.
2 Gets hit by BB on the caster's turn.
3 Chooses to move away on his turn (ie a different turn entirely).
4 Step 3 provokes an OA, gets hit.
5 Chooses at that point to stop moving without triggering the pre-existing BB.

If, instead, the situation is
1. Target within reach
2. Moves away, provoking an OA
3. Is hit by War Caster-cast BB
4. Stops moving (out of reach, but not having moved after being hit by the reaction-BB)
5. Doesn't trigger BB

Then we're in total agreement. In that case, he'd have to move more (which is his option to do or not to do). But I'd been thinking of the prior case, where the BB pre-existed the target's movement/triggering the OA.

[Arkhios]

Maybe I misunderstood? I was under the impression that the case at hand was
1 Target within reach.
2 Gets hit by BB on the caster's turn.
3 Chooses to move away on his turn (ie a different turn entirely).
4 Step 3 provokes an OA, gets hit.
5 Chooses at that point to stop moving without triggering the pre-existing BB.

If, instead, the situation is
1. Target within reach
2. Moves away, provoking an OA
3. Is hit by War Caster-cast BB
4. Stops moving (out of reach, but not having moved after being hit by the reaction-BB)
5. Doesn't trigger BB

Then we're in total agreement. In that case, he'd have to move more (which is his option to do or not to do). But I'd been thinking of the prior case, where the BB pre-existed the target's movement/triggering the OA.

Maybe I wasn't clear on my intent. Good to know we are in agreement. I was talking about the case that the target was not already under the effect of an earlier BB hit, because I thought that was what was being discussed. Apologies.

Perhaps I should go to sleep.

[PhoenixPhyre]

Maybe I wasn't clear on my intent. Good to know we are in agreement. I was talking about the case that the target was not already under the effect of an earlier BB hit, because I thought that was what was being discussed. Apologies.

Perhaps I should go to sleep.

Not a problem. I tend to miss some context switches at time, especially when I'm looking at things from the phone while waiting for things to compile.

[Talamare]

OA triggers as soon as the target moves away from your reach (farther than 5 ft). By then, they're already in the next 5ft. window, whether or not they choose to move further. But that's besides the point. It doesn't matter how far beyond they moved. What matters is that the BB does not trigger from the same movement that already triggered OA, UNLESS THE TARGET CONTINUES THEIR MOVEMENT AFTER BEING HIT BY BB. You resolve the attack roll to hit with BB first, and only after that the rider effect of the spell itself. But the target can choose not to move an inch further after being hit (whether or not we're using a 5' grid).

You're willfully ignoring what I said. Stop that.

Well not exactly...

If you have Sentinel, they provoke and you hit; they don't leave the space.
Since AOO hits happen before they actually leave the space.

Also, this isn't targeted at you, but "Move" in DnD is moving to another square 5'/1m Grid; They can dance all they want to in their own square without Booming.

[Greywander]

You don't declare a move, you move. And once you've done so, you can't take it back. You can't say "oh, I'm going to step back" and then, when hit with an OA, not step back.

Since movement is not an action in this edition, one can split their movement within their turn however they please. Even stop moving immediately after they're hit by Booming Blade (assuming they know what it does, which is an entirely different question whether they should know).
I think this is what makes the difference. If, for example, I interpret Shield Master to allow one to BA shove first, then take the Attack action, then by shoving you are already committed to taking the Attack action and can't take it back. You can't do a "partial" Attack action and then use the rest of your action for something else. An action is all or nothing.

But movement is different. I can move any number of feet (including 0 feet), stop, move some more, stop, move some more, etc. up to whatever my speed is. So I believe that if you choose to move and have that movement interrupted before it occurs, then you can decide to go ahead and stop moving. There is no minimum number of feet you have to move when you decide to spend movement.

Another aspect of this is that attacks are (in my interpretation) instantaneous. When an attack occurs, time essentially stops until that attack is resolved. Handling it this way causes a lot of "problems" to go away, e.g. you can only attack with a weapon you are wielding, which requires the weapon to be held, but a thrown weapon is not being held at the instant it does damage. If the act of attacking with a thrown weapon is instantaneous, then you are, in fact, holding the weapon when you attack with it, and after the attack has been resolved, then the weapon is no longer in your hand.

And I suppose the third part of this is the order of operations. Attacks are instantaneous, but movement is sequential. You move to A, then take an action, then move to B, then take another action (e.g. bonus action, Extra Attack), then move to C, etc. Movement has an order to it, you don't just instantly teleport to the final space you end your turn on, nor do you simultaneously occupy every single square you move through at the same time (though this is one way to handle simultaneous turns). Because attacks are instantaneous, they can't occur simultaneously with movement. Movement stops when an attack occurs, and resumes once the attack is resolved.

In order to make an OA, the target must be within the reach of your weapon, but an OA is only triggered when a creature moves out of your reach. If any part of the movement happens before the attack, then the target is out of range and can't be targeted. However, this is clearly a wrong interpretation, as it means OAs would never occur, since the target would always be out of range. So the movement can't happen before the attack. And because the attack is instantaneous, movement can't happen during the attack. This must mean that movement has to happen after the attack. And since there's no minimum distance you're required to move, you can decide to just stop moving immediately.

I'm honestly not sure how much of this is actual RAW and how much is just my own interpretation, but this just seems like an easier way to run it and makes more sense.

Also, I feel like people are once again forgetting that Booming Blade is meant to be a control spell; you want the enemy to not move. Now, it's true that for some builds it's just a way to get extra damage on a single attack, and it's also true that forcing an enemy to stand still isn't always advantageous to you, but there are things you can do, both in how you build your character and how you play them, that can make it more advantageous more often if the enemy is forced to stand still.

I guess what I'm trying to say is that Booming Blade is fine as a bit of extra damage, but if you're fully utilizing the spell to its true potential, then your primary goal is usually to hold the enemy in place, and the secondary damage is a consolation for if they move anyway. In other words your build and/or playstyle make forcing the enemy to stand still a better outcome than dealing the extra damage. The idea is to stab the enemy with Morton's Fork (https://tvtropes.org/pmwiki/pmwiki.php/Main/MortonsFork), where moving is bad for them (because they take damage), but not moving is also bad for them, so no matter what they do, they're screwed.

It's also worth pointing out that if you use Warcaster to replace an OA with a spell, such as Booming Blade, then you're no longer making an OA. Thus, Sentinel never triggers and reduces speed to 0. But Booming Blade deals more damage than an OA would, so it's a trade-off. You can make a normal OA and be certain that the enemy won't be able to move, or you can use Booming Blade and deal extra damage while offering the enemy the choice to move at the cost of even more damage. With that in mind, if you're primarily replacing OAs with Booming Blade, then you can probably skip getting Sentinel.

[Witty Username]

So, checking the book, I think the order follows:
1. Opportunity attack, since it is before they leave reach (opted to replace with a booming blade)
2. (Assuming a hit) Creature now has 2 booming blade effects, 1 suppressed due to stacking effects
3. Creature completes its move, boom trigger
4. Creature has 1 booming blade effect, no longer suppressed as the other ended.

So if the creature moves another 5ft, second boom trigger.
This is assuming the combining spell effects indicates that they can't trigger both effects simultaneously one would have to take priority, but since the second couldn't trigger it also couldn't be ended by the 5ft of movement.

[Smersh_23]

Combining Magical Effects php 205
The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect—such as the highest bonus—from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

1. BB is proc'd after the OoA is resolved and the 5 foot movement is completed.
2. Only one of the BB's can proc since the rule states that the most recent casting of the same potency applies. The first casting of BB is still active until the duration expires.
3. Im not sure of RAW for this one, as DM I would rule that if you declared your moving 5 feet, you are moving 5 feet unless some other effect stops your movement. So in this case, if the target moved an additional 5 feet beyond the initial trigging of the AoO and the second casting of BB from warcaster feat, the very first BB would then proc so the target can get hit by both BBs. The target just cant get hit by both BB's in the same 5 foot of movement.

[Talamare]

OAs happen at the edge of the square they started in, but BEFORE they leave the square

Everyone has full control of their character, they may choose to stop before they leave it. I posted the Sage Advice on this already


So, once again.

1 - They move to leave
2 - OA Triggers
2.1 - If they have Boom on them- Hits or Misses, Boom can't stack.
2.2 - If they didn't have Boom on them- they now have a Stack
3 - Assuming movement if they have a Boom Stack
3.1 - They decide to move, They will trigger Boom
3.2 - They decide to stay, They will still be at their starting point. Doesn't trigger Boom. Congratulations you kept the enemy from running away.
3.3 - They decide to stay, but do an interpretive dance on how much they hate you. Doesn't trigger Boom.
3.4 - They have an effect that forces them to move away, such as a Push... Doesn't trigger Boom.
3.5 - They have an effect that compels them to move away, such as Command or Dissonant Whispers... Doesn't trigger Boom.
3.6 - They decide to stay, but then teleport away... Doesn't trigger Boom.

Edit
3.7 - They don't have a magical effect that forces them to move away, but they have a social effect that pressures them into moving away... Technically Does trigger Boom.

Example, you put Booming Blade on a parent, then kidnap their children from across the way and tell them that you will kill their children if they don't move...

[da newt]

I've always used the following order of operations:

creature w/ BB effect on it decides to move
- do you move out of the current square? This triggers the BB rider damage.
- do you move into a square outside the reach of your foe? This triggers the OpAtt.
OpAtt hits w/ BB, and creature occupies the next square
- do you move out of the current square? This triggers the 2nd BB rider damage.

I'm not sure this is strictly RAW, but it's logical and easy to rule objectively every time, it allows the creature to exercise agency at every decision point, and it covers the alternate situation where the creature moves out of it's current position but into a position that is still within the foe's reach.

[Segev]

Your reach is (probably) five feet from your square. Most creatures will be some number of feet further than than zero away from the edge of your square when fighting "in your reach." On average, they will be about 2.5 feet into their own square.

OAs trigger when a creature leaves your reach. This means when they step from five feet from the edge of your square to six feet from the edge of your square. Technically, on average, this will be after about 2.5 feet of movement.

Booming Blade triggers when the target voluntarily moves at least five feet. This will happen generally after they leave your reach, unless they started directly on the edge of your square.

So, under most common circumstances, the target will trigger the OA before it triggers Booming Blade's malus. If the target was truly right on the edge of your space, then the target triggers them simultaneously, and the DM decides the order of resolution, though I believe he is encouraged to allow the player controlling the relevant effects (i.e. you) to determine it in those cases.

If the creature is closer than the edge of your square, it obviously occupies your square, to square-based triggers already tell us the creature triggers the secondary thunder damage before leaving your reach.