That hit even more dangerous than one on a QB in the pocket, that's the kind of hit that could kill someone, guy running full speed gets blasted helmet to helmet.
Here’s the easiest way to judge OPI....if on the route the receiver is on he’s even with the DB for 10-20 or more yards and then all of a sudden the receiver has 3-4 yards of separation when the ball comes in he either pushed off or the DB fell on his face. Nobody has the agility to get that separation instantly with their stride.