Many unwritten regulations in the game of hockey include not shooting the puck after the whistle, not striking or bumping the goalie, and many others. These unwritten rules are more of a "respect factor" among all hockey players.
The unwritten rule that you shouldn't hit the goalkeeper was recently breached, and cruelly.
So severely that his own team feels he should have received greater punishment than he did, even though the punishment he received was pretty severe�he was jumped by the whole opposition team.