[U52]

I had a coach approach me last night about the rules of a crackback block and when it is legal and illegal. The week before his team was flaged for not giving the defensive player time to turn and protect himself for such a block. I looked up the rules in the Redding book and found no such ruling as far as giving the defensive player time to turn. I did find that 1. The block must be above the waist and 2. The head of A must be in the front of D. Did I miss anything else ?