Rapper pitbull punches and knocks a guy out mid-song, then keeps singing like nothing happened

Watch this amazing video from a show of a rapper called Pitbull (here's his myspace) what happens is some guy starts throwing money at him while he's singing. Pitbull then calls the guy up on stage, even helps him up. When the guy keeps showering Pitbull with money, he punches him all of a sudden, and knocks him out. This, while keeping the mic and singing. The guy falls down, a security guy pushes Pitbull back, and Pitbull, really cool, keeps singing his tune.