Andy Gilder wrote:
Probably because the hand off is basically a flat of the hand delivered front on to the face/head and isn't likely to do a great deal of damage. .
I once turned out for our company team in a local 5-a side footy league. Running down the boards with the ball I instinctively handed off the guy behind me and made a serious mess of his nose. Blood everywhere, probably broke it too. Funniest part was the ref who waved play on shouting "accidental, accidental".