I've noticed that if a player blocks a shot, but the ball is still in the offensive players hand, it is often called a foul, especially if it's a fast break lay-up attempt. I know this is hard to see, but I think the offensive player gets the nod on the call, more times than not. Fair? It looks like a lot of legit blocks are called fouls to me.
alot of the time it's usually a foul on the body. like over the back or the off-hand (non blocking) is holding the guys shoulder or body to get the extension to block it.