The rule is as follows:
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 with the helmet, forearm, hand, fist, elbow or shoulder. When in question, it is a foul (Rules 2-27-14 and 9-6). (A.R. 9-1- 4-I-VI)
A couple of things to note:
1. If the player is defenseless, helmet to helmet is illegal, regardless of whether it is the crown or the facemask.
2. If it's in question, the ref's are instructed by rule to throw the flag.
Gotsis call stunk for us, and changed the game, but was probably the right call per point 2 of the rule.