Actually it does matter:
"No player shall target and make
forcible contact to the head or neck area of a defenseless opponent (See Note 2 below)
with the helmet, forearm, hand, fist, elbow or shoulder. This foul requires that there be at least one indicator of targeting (See Note 1 below). When in question, it is a foul (Rules 2-27-14 and 9-6). (A.R. 9-1-4-I-VI)"
"
Note 2: Defenseless player (Rule 2-27-14):
- A player in the act of or just after throwing a pass.
- A receiver attempting to catch a forward pass or in position to receive a backward pass, or one who has completed a catch and has not had time to protect himself or has not clearly become a ball carrier.
- A kicker in the act of or just after kicking a ball, or during the kick or the return.
- A kick returner attempting to catch or recover a kick, or one who has completed a catch or recovery and has not had time to protect himself or has not clearly become a ball carrier.
- A player on the ground.
- A player obviously out of the play.
- A player who receives a blind-side block.
- A ball carrier already in the grasp of an opponent and whose forward progress has been stopped.
- A quarterback any time after a change of possession.
- A ball carrier who has obviously given himself up and is sliding feet-first"