Booming Blade

Action | 5 ft | V/S/M | Instantaneous
You make a melee attack with a weapon. On a hit, the target takes normal weapon damage, plus booming energy. Until the start of your next turn, if the target willingly moves 5 feet or more, it takes 1d8 thunder damage, and the spell ends.

At higher levels:
5th level: +1d8 thunder damage on hit, 2d8 for movement.
11th level: +2d8 thunder damage on hit, 3d8 for movement.
17th level: +3d8 thunder damage on hit, 4d8 for movement.