Early in the fourth quarter of Thursday night’s Saints-Cowboys game, Drew Brees threw a third-and-long screen pass underneath to Alvin Kamara. Kamara scampered eight yards up the right side, where he was met by Cowboys linebacker Jaylon Smith, who launched himself head-first at Kamara’s helmet.

As expressed by Troy Aikman and Mike Pereira, the hit appeared to be a pretty clear violation of the NFL’s new helmet rule, which prohibits using the helmet to “butt, spear, or ram an opponent.” But even if you don’t know the specific language of the helmet rule, you intuitively know that if there is a rule commonly referred to as “the helmet rule,” it must surely exist to discourage exactly this sort of hit. Kamara was knocked from the game and eventually had to be taken to the Saints locker room.