Player safety is a hot topic after several Week 6 helmet-to-helmet incidents. Here’s the section in the NFL rulebook on unnecessary roughness
Rule 12, Section 2, Article 8 (Unnecessary roughness) in the NFL rulebook
(f) If a player uses any part of his helmet (including the top/crown and forehead/”hairline” parts) or facemask to butt, spear, or ram an opponent violently or unnecessarily. Although such violent or unnecessary use of the helmet and facemask is impermissible against any opponent, game officials will give special attention in administering this rule to protecting those players who are in virtually defenseless postures, including but not limited to:
(1) Forcibly hitting the defenseless player’s head, neck, or face with the helmet or facemask, regardless of whether the defensive player also uses his arms to tackle the defenseless player by encircling or grasping him; or
(2) Lowering the head and violently or unnecessarily making forcible contact with the “hairline” or forehead part of the helmet against any part of the defenseless player’s body; or
(3) “Launching” (springing forward and upward) into a defenseless player, or otherwise striking him in a way that causes the defensive player’s helmet or facemask to forcibly strike the defenseless player’s head, neck, or face—even if the initial contact of the defender’s helmet or facemask is lower than the defenseless player’s neck. (Examples: a defender buries his facemask into a defenseless player’s high chest area, but the defender’s trajectory as he leaps into the defenseless player causes the defender’s helmet to strike the defenseless player violently in the head or face; or a defender, using a face-on posture or with his head slightly lowered, hits a defenseless player in an area below the defenseless player’s neck, then the defender’s head moves upward, resulting in strong contact by the defender’s mask or helmet with the defenseless player’s head, neck, or face [an example is the so-called “dip and rip” technique]).
Note: The provisions of section (f) do not prohibit incidental contact by the mask or noncrown parts of the helmet in the course of a conventional tackle on an opponent.
(g) if the initial force of the contact by a defender’s helmet (including facemask), forearm, or shoulder is to the head or neck area of a defenseless player.
Note: Defenseless players in (f) and (g) shall include (i) a player in the act of or just after throwing a pass; (ii) a receiver catching or attempting to catch a pass; (iii) a runner already in the grasp of a tackler and whose forward progress has been stopped; (iv) a kickoff or punt returner attempting to field a kick in the air; and (v) a player on the ground at the end of a play.
h) If a receiver has completed a catch and has not had time to protect himself, a defensive player is prohibited from launching (springing forward and upward) into him in a way that causes the defensive player’s helmet, facemask, shoulder, or forearm to forcibly strike the receiver’s head or neck area—even if the initial contact of the defender’s helmet, facemask, shoulder, or forearm is lower than the receiver’s neck.
Note: Launching is defined as springing forward and upward by a player who leaves his feet to make contact on the receiver.
(i) a kicker/punter, who is standing still or fading backwards after the ball has been kicked, is out of the play and must not be unnecessarily contacted by the receiving team through the end of the play or until he assumes a distinctly defensive position. During the kick or during the return, if the initial force of the contact by a defender’s helmet (including facemask), forearm, or shoulder is to the head or neck area of the kicker/punter, it is a foul.
(j) any player who grabs a helmet opening of an opponent and forcibly twists, turns, or pulls his head.
(k) Illegal contact with the helmet against the knee of the snapper during an attempt for a field goal or kick try.
Penalty: For unnecessary roughness: Loss of 15 yards. The player may be disqualified if the action is judged by the official(s) to be flagrant.
Note: If in doubt about a roughness call or potentially dangerous tactics, the covering official(s) should always call unnecessary roughness.