This is a clip of a flying punch, more commonly known as the Superman punch, in an mixed martial arts match between Savant Young (a.k.a. Black Superman) and Ed West. I originally wanted to find a clip of George St. Pierre smacking down Matt Hughes with it in their rematch, but I couldn't find it online.

The Superman punch is called a cobra punch in Muay Thai, due to the setup movement of the attacking fighter. To set up the strike, the fighter will rear back as if he is about to throw a high round kick or, as in this case, a high or flying knee with the rear leg. Then, instead of throwing the rear leg strike, he shoots his rear leg backwards while throwing his upper body forward, in a pendulum-type movement. He follows this momentum by jumping forward on his left leg, going into a diagonal Superman-type position, and then throws the rear straight or overhand punch with a shoulder twist.

The Superman punch, as with all flying attacks, is a relatively low-percentage technique, but it is extremely entertaining to watch, and when it lands, it feels like you've been hit with a ton of bricks. Also, like all flying attacks, it has the advantage of being an overwhelming and surprising attack, and is a good trick to have in one's striking arsenal.