See the penalty from start to finish......if there is a player blocking your view and your view is interrupted ...See the penalty from start to finish.
I threw a block in the back flag on a screen pass while I was at the LOS. You see the track start and can almost read the player's mind. 26 launched, then suddenly a receiver blocked my view. 26 was headed in one direction and 82 in another falling away from each other. My hand was ready grabbing my flag. Flag out and I immediately thought, I was blocked from seeing contact. Runner down stooped the clock made sure the Umpire had the spot, then ran immediately to the only set of eyes looking at the action from the backside of the play. One question "Did 26 hit 82 from behind?" "No he missed, 26 left his feet to block and 82 tripped, there was no contact." "Wave off my flag, I'll explain at halftime."