BTW, this is a good article where the NHL tried to clarify the head shot rule:
What makes a hit illegal? That's the question the NHL sought to clarify in a video posted on Thursday in wake of three controversial checks — two of which led to suspensions.
www.sportsnet.ca
"In the video, the NHL said the head must be the main point of contact — not necessarily the first point of contact — and that said head contact must have been avoidable for a hit to qualify as illegal.
Whitecloud's hit on Knies was deemed legal since it did not meet the first criteria.
"While there is inarguably head contact here, we see Knies' entire body stopped in its tracks and driven backwards simultaneously with his head in a way that indicates the body absorbed the force of this check," the NHL said in the video."
and
"Meanwhile, Boeser's and Nurse's heads were considered by the NHL to have taken the brunt of the impact in Jeannot's and Reaves' hits, while the perpetrators' "poor angle of approach" meant the head was avoidable.
"Both players cut along the front of their opponents' core rather than hitting through their shoulder or chest, which causes the contact to be directly and forcefully with their opponents' heads," the NHL said. The NHL noted that Whitecloud, on the other hand, takes a proper angle and "does not elevate up excessively or unnecessarily to pick the head as he delivers the check.""
The Cizikas hit was similar to the Whitecloud hit, IMO.