Note that "leading with the helmet" in this instance does not specify leading with the crown of the helmet.

Targeting and Making Forcible Contact to Head
or Neck Area of a Defenseless Player

ARTICLE 4 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) (AR 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 their 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