[RPG] Does the Booming Blade spell’s damage from moving trigger before or after an opportunity attack


I hit an enemy with booming blade, and before my next turn they chose to move away, provoking an opportunity attack. Does the booming blade's damage-on-movement trigger before or after I make my opportunity attack?

Best Answer

The Booming Blade effect triggers before the opportunity attack.

Booming Blade states:

If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends.

Opportunity Attack states:

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 interrupts the provoking creature’s movement, occurring right before the creature leaves your reach.

Emphasis mine

The creature first begins to move, triggering the Booming Blade and then, right before it leaves your reach, the opportunity attack triggers.

Of course this is all assuming you have not spent your reaction, your reach is 5ft and the enemy attempts to immediately leave your reach instead of moving around you.