Do you have a direct link to the video?
http://www.youtube.com/watch?v=GVW5_PJHzR4&NR
Here it is - I think. Of course I don't know what all was going on prior to this , but it appears they had him restrained and the cop just kept on punching him in the face. I don't see what he was doing to warrant him being punched in the face at that point.