Corrected entry: In the first round of the boxing match it is obvious that Tarver does not hit Stallone, but only gets close and then a sound effect signifies the punch. The sound is the same every time, and Stallone doesn't move like he would have if he'd been hit. Later in the fight the punches look more realistic.
Jacob La Cour
28th Dec 2006
Correction: Most if not all of the punches thrown are real. Sly stated this in the commentary and also you see it in the "making of" video. He wanted to make it as real as possible.