There’s a difference between something violating the rules of a sport and it rising to the level of a criminal act.
To use your example, hitting is a part of hockey. Hitting someone in the head is against the rules and will lead to a penalty/suspension, but in a fast-paced sport where hitting is legal contact to the head is inevitable and represents an obvious risk that is accepted by those who chose to participate. So as long as that contact occurs during the normal course of play and via a reasonable hockey action it would be absurd to argue for criminal charges.
Now if it’s ten seconds after the whistle, everyone is skating around slowly, and it’s clear to any reasonable person that play has stopped, and a player suddenly skates up to another with speed and gives him a blindside forearm shiver to the head? That might well constitute assault.
Or for a different example that is more relevant to the case under discussion, high sticking is a penalty, but an accidental high stick that occurs during the course of play isn’t a criminal act. An intentional two-handed baseball swing into somebody’s head clearly is. Here the distinction is made not on timing but rather on the latter being an intentional action that is both grossly reckless and well outside the accepted bounds of sporting activity. It matters not if the swinger only intended to hit his opponent on the torso and never meant for his stick to go as high as it did.
So is intentionally kicking an opponent with one’s skate an accepted part of hockey? Clearly it is not. So the question then is did it happen accidentally or was the kick intentional, even if the location and outcome weren’t? If the latter then that would indeed be a criminal act.