My thought is that if hard hits like that, where Tkachuk wound up to a freight train when he hit Kassian at the side of the goal, and then retreated in a hurry to admire his own work. To me it seems like a intent to injure, and players will get injured from heavy hits, especially those that are not seen coming. It is up to the NHL to decide what is allowed. Kassian's reaction is understandable, but he failed to control his anger