While there is a pretty thick rule book for hockey, there is also some unwritten rules not in the book that the players follow.
One of the most well known is that no player is to shoot the puck after the whistle, but definitely not try to shoot it into the other teams net/goalie and well, Sanheim broke that rule.
In the third period of last nights game between the Flyers and Flames, Sanheim took a shot at Jacob Markstrom after the whistle had blown.
The Flames were not happy about this and went after him: