D&D 5E Dissonant Whispers + Warcaster + Booming Blade AOO mechanics

[Ruin Explorer]

Booming blade specifies "if the target willingly moves". Movement over which the target doesn't have a choice does not trigger the effect. Running from a failed Dissonant Whispers save is no more willing than movement by being shoved.

This is absolutely correct, rules-wise, both RAW and RAI.

However, the problem is that Booming Blade is a profoundly "4th edition-style" spell in 5th edition, and the entire concept of "willing movement" vs "forced movement" is not something 5E generally thinks about, whereas it was a big deal in 4E. Looking at discussion on this, here and elsewhere, it's clear that a lot of people see "willing" vs "forced" as more "your mind does it" vs "a physical outside force acts on you" - so they see fear and confusion-based movement as "willing" movement.

And I feel like, for 5E, that's kind of probably a better distinction, even though for 4E, which was a much tighter game on the field, and where there were stronger "meta" elements, that made sense.

Booming Blade causes a particular issue both because it's a 4E-style wording, and because conceptually, it's based on you moving out of the "sheath of energy", which obviously you running away would do.

 

[Ancalagon]

Yes! I see this unstable sheath of energy as "sticking" to the person, when they are tossed around by a force effect or shoved by a giant, or standing on a moving ship for that manner. If they move on their own power, kapow!

That being said... It's my ruling, it's one others may like too, but of course not everyone would agree with this - perhaps even a majority. And that's ok - each table is different.

(for example, in one gaming group I'm in, a familiar assist takes a bonus action)

 

[Clint_L]

Yeah, absolutely you gotta do what works for you, and that's how should be.

I would rule the same as Umbran, though. The text seems pretty straightforward in this case.

 

[Gorck]

To answer the initial question posed by @ECMO3, if the DM deemed that the creature's fleeing caused by Dissonant Whispers was "unwilling" movement and did not trigger the secondary thunder damage, then I would say that the "booming energy" stays on the creature instead of dissipating. To me, the term "sheathed" implies that it adheres to the creature, rather than being some sort of cloud that the creature is standing in.