Popularized by balla rapper,Juvenile. It's meaning, in all respects, is not even known to those who have witnessed this event.
Basically it's when the black booty be droppin on the dance floor, which could be at any party in which Juvenile or other rap music is being bumped. In certain cases bystanders are injured by the bouncing booty.
"Tommy witnessed the Nolla Clap last night...he's still dazed and confused."
"Damn homie! Did ya see Shaniquah doing tha NOLLA CLAP last night?! She took out Andy with that phat booty!"