D&D 5E Using booming blade on a reaction attack with sanctuary question

[Maxperson]

This is contrary to what the rules say. You can't make an opportunity attack against an enemy that is within your reach. If he triggered the AOO then he must be outside your reach. The fact that you can make an attack against an enemy beyond your reach is a case of specific rule for AOOs vs general rule for attacks.

The AOO caused by leaving reach actually occurs right before the creature exits. It interrupts him in the middle of his action, one of the very few ways to interrupt an action before the trigger completes, and then it leaves reach.

So the sequence of that is.

1. Creature is leaving reach.
2. AOO triggers and you attack.
3. Creature leaves reach and is now 5 feat away.

 

[Krachek]

This is contrary to what the rules say. You can't make an opportunity attack against an enemy that is within your reach. If he triggered the AOO then he must be outside your reach. The fact that you can make an attack against an enemy beyond your reach is a case of specific rule for AOOs vs general rule for attacks.

Extensible arms nice.

 

[ECMO3]

If your DM rules that you can cast Booming Blade instead of making an attack when the enemy provokes an opportunity attack from you (which is not normally possible), and you hit with it, the enemy would theoretically take the damage from both instances of the spell.

Thanks for the clarification on just before leaving reach.
Regarding what is quoted, I have warcaster, so I can cast a spell on an enemy that causes an oppotunity attack.

 

[Charlaquin]

Thanks for the clarification on just before leaving reach.

No problem!

Regarding what is quoted, I have warcaster, so I can cast a spell on an enemy that causes an oppotunity attack.

I guessed that might be the case. In my reading of Booming Blade, it’s not a valid spell to cast via Warcaster, but it’s worded ambiguously enough I can easily see how one would come to a different conclusion. And it’s not really relevant to the origin question anyway.

 

[ECMO3]

No problem!

I guessed that might be the case. In my reading of Booming Blade, it’s not a valid spell to cast via Warcaster, but it’s worded ambiguously enough I can easily see how one would come to a different conclusion. And it’s not really relevant to the origin question anyway.

Why not?

"When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature."

It is a spell with a casting time of 1 action, only targeting 1 creature. I would think green flame blade is not doable since it targets 2 creatures, but booming blade should be ok I think.

 

[Charlaquin]

Why not?

"When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature."

It is a spell with a casting time of 1 action, only targeting 1 creature. I would think green flame blade is not doable since it targets 2 creatures, but booming blade should be ok I think.

Booming blade doesn’t target an enemy. It has a range of “self” and the effect of allowing you to make a melee weapon attack with the weapon used for the material component, which has a special effect if it hits.

Like I said, it’s ambiguous enough that I can see how someone might interpret it differently, and it’s not really relevant to the topic. But that’s my understanding of how Booming Blade works.

 

[Blue]

Getting back to the original question, we do have to see when the first BB goes off. Because layering a second BB on before the damage goes off will only leave one damage as two spells of the same name overlap, not stack.

 

[cbwjm]

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.

Bold added for emphasis.

Since the attack occurs before the creature leaves your reach, I would rule that the sequence goes:

1. The enemy begins to move out of your reach
1a. Right before the enemy moves out of your reach, you make an opportunity attack
1b. Sanctuary ends due to you making an attack
2. The enemy finishes its movement
3. The enemy takes damage from Booming Blade

If your DM rules that you can cast Booming Blade instead of making an attack when the enemy provokes an opportunity attack from you (which is not normally possible), and you hit with it, the enemy would theoretically take the damage from both instances of the spell.

I probably should have read that again sooner. Sentinel always seemed a little off to me, but makes sense to me now having read the final sentence.

 

[Charlaquin]

Getting back to the original question, we do have to see when the first BB goes off. Because layering a second BB on before the damage goes off will only leave one damage as two spells of the same name overlap, not stack.

Oh, that’s a good point!

Actually, looking at booming blade again, the damage triggers when the target moves 5 feet or more. If one wanted to be really nit picky about it, you could say that the second instance of booming blade “occurring right before the creature leaves your reach” would the distance between where they are when the attack happens and where they end up after is fewer that 5 feet. But I think the cleaner ruling is just to say both instances are triggered when the creature leaves your reach.

 

[Nikosandros]

Somewhat related to the question at hand: do you people allow someone who has been targeted by an OA triggered by leaving reach to interrupt their movement and decide to remain where they are?