Booming blade - how does it crit, and is this legit?

[Harzel]

So are you saying that you would be able to avoid Booming Blade damage by just roleplaying being scared?

It can't just be 'scared'; it has to be 'so scared as to overwhelm volition'.

If the player
a) can justify the character's overwhelming fear by either citing an element of the PC's background or establishing a hitherto unknown character trait;
AND
b) is willing to have the character act as if it has been affected by the Fear spell,
then, yes, I would probably allow it.

If the player wants to declare that the PC is scared, moves 10 ft., and then is not scared - not so much.

 

[Ancalagon]

My take is that the booming energy manifests in the brain. So it dors not have to be sentient but it is just zapping you if your brain sends signals to your muscles not a spell that overrides your brain function.

... but a spell that makes you afraid and run away makes your brain send signal to your muscles... it doesn't move your legs for you like some kind of elaborate force effect.

 

[McRippy]

RAW states that damage die are doubled on a crit. Since 1d8 is a damage die, it would be doubled under crit rules RAW. And since it was applied on the PCs turn of combat, the double damage die would apply.

Ways around this: creatures with thunder resistance, creatures with range attacks, making booming blade a 1st level spell instead of a cantrip, banning swashbuckler/hexblade multiclassing, making attack action with booming blade override cunning action, etc etc. Its not hard to deal with tbh as a DM