The NHL have introduced a new rule on fighting, which means players cannot remove their helmets prior to a fight (entire rule below).
While a more effective rule might be: "fighting will result in a lengthy ban", punch-ups are so engrained in the game that players have already found a loophole before the season has even started.
New York Islanders player Brett Gallant and Krys Barch of the New Jersey Devils squared up to each other three times on Thursday night, but at least they employed gentlemen's rules. Before the second bout, each player ludicrously removed the other's helmet to get around the rule and shorten their penalties.
From rule 46.6:
No player may remove his helmet prior to engaging in a fight. If he should do so, he shall be assessed a two minute minor penalty for unsportsmanlike conduct. Helmets that come off in the course of and resulting from the altercation will not result in a penalty to either player.
Via Puck Daddy