LOL, you just made me think of something... Remember how the older cars had chrome bumpers? Then the engineers figured out how the collapsible bumpers were safer, taking the energy out of the collision. If a NASCAR car has a wreck, if flies to pieces, based on the same thing.
SO- Maybe just make helmets that fly apart when guys get speared. Saves the refs having to make a judgement call!
“Helmet disintegration, number 62. Player will be ejected from the game, and a new helmet ordered at his expense. 15 yards, 1st down!” The ref’s motion would be putting his fists on his head, throwing them out quickly while spreading his fingers... :-D
Or, if your helmet cracks, you’re done.