[just another ref]

Originally Posted by JRutledge

You do not have to call anything if you choose not to. If the only reason we are calling fouls are because of the amount of the contact, then we are not following the rules as written as so many people here want to suggest we must do all the time under every circumstances.

Peace

I already quoted the rule which I see as applicable.

Originally Posted by just another ref

4-27-5: If, however, a player approaches an opponent from behind or from a position from which he has no reasonable chance to play the ball without making contact with the opponent, the responsibility is on the player in the unfavorable position.

That's exactly what happened here. When you knock a guy to the floor while executing a "clean block" it is no longer clean.