By Definition is.......Hitting a "defenseless" opponent ABOVE the shoulders, or USING THE CROWN OF THE HELMET to contact an opponent.

Well, back when I played football in HS and College we called it an "Ear Hole" hit. You put your face mask "through" the ear hole of a player looking the other way.
It was a great way to get "Hit OF The Week".

Basically, College and the NFL are ELIMINATING that type of hit, or any collision where the defensive player "uses" his helmet.....That's Great for the game!

Lastly......Even though its was a devastating hit.....A safety for LSU had a WIDE OPEN rib shot to the WR going up for a high pass. He put his shoulder in the "sweet spot" just between the shoulder and rib cage.....It was one heck of a hit, pretty much a defenseless player, BUT within the rules of the game...He did not lead with his helmet.