Rule 9 - ARTICLE 3
Targeting and Making Forcible Contact With the Crown of the Helmet
    - No player shall target and make forcible contact against an opponent
      with the crown (top) of his helmet.
    - This foul requires that there be at least one indicator of targeting
      (See Note 1 below).
    - When in question, it is a foul. (Rule 9-6) (A.R. 9-1-3-I)

Rule 9 - ARTICLE 4.
Targeting and Making Forcible Contact to Head or Neck Area of a Defenseless Player
    - 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 1:
    - “Targeting” means that a player takes aim at an opponent for purposes of
      attacking with forcible contact that goes beyond making a legal tackle or a
      legal block or playing the ball.
    - Some indicators of targeting include but are not limited to:
         - Launch - a player leaving his feet to attack an opponent by an upward and forward
           thrust of the body to make forcible contact in the head or neck area
         - A crouch followed by an upward and forward thrust to attack with forcible contact
           at the head or neck area, even though one or both feet are still on the ground
         - Leading with helmet, shoulder, forearm, fist, hand or elbow to attack with forcible
           contact at the head or neck area
         - Lowering the head before attacking by initiating forcible contact
           with the crown of the helmet

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