Trevathan suspended 2 games

From the NFL rulebook. You can argue that he had no ill intent and therefore the hit wasn't "dirty", but it was certainly against the rules.

SECTION 2 PERSONAL FOULS

ARTICLE 7. PLAYERS IN A DEFENSELESS POSTURE.

It is a foul if a player initiates unnecessary contact against a player who is in a defenseless posture.

(a) Players in a defenseless posture are:

                            (5) A runner already in the grasp of a tackler and whose forward progress has been stopped.

(b) Prohibited contact against a player who is in a defenseless posture is:

(1) forcibly hitting the defenseless player’s head or neck area with the helmet, facemask, forearm, or shoulder, even if the initial contact is lower than the player’s neck, and regardless of whether the defensive player also uses his arms to tackle the defenseless player by encircling or grasping him

(2) lowering the head and making forcible contact with the crown or “hairline” parts of the helmet against any part of the defenseless player’s body

Penalty: For unnecessary roughness: Loss of 15 yards and an automatic first down. The player may be disqualified if the action is judged by the official(s) to be flagrant.

ARTICLE 8. INITIATING CONTACT WITH THE CROWN OF THE HELMET.

It is a foul if a runner or tackler initiates forcible contact by delivering a blow with the top/crown of his helmet against an opponent when both players are clearly outside the tackle box (an area extending from tackle to tackle and from three yards beyond the line of scrimmage to the offensive team’s end line). Incidental contact by the helmet of a runner or tackler against an opponent shall not be a foul. Note: The tackle box no longer exists once the ball leaves the tackle box.

Penalty: Loss of 15 yards. If the foul is by the defense, it is also an automatic first down. The player may be disqualified if the action is flagrant.

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