(VIDEO): Kunitz breaks one of hockey's unwritten rules, Flyers retaliate.

It's an unwritten rule in hockey that you do not shoot the puck at the empty net on a delayed penalty. Unfortunately for Chris Kunitz, he didn't get that memo. In Sunday afternoon's rivalry matchup between the Pittsburgh Penguins and Philadelphia Flyers, the Penguins were charged with a penalty. After a lengthy delayed call, the puck finally lands on Chris Kunitz's blade. He proceeds to fire a slapper right at the Flyers open cage and the puck ricochets off the post. This had the Flyers in a frenzy and sparked an unruly scrum between the two teams, who have no love lost. Kunitz should definitely know better.

#GottaSeeIt: #Penguins forward Chris Kunitz broke one of hockey's unwritten rules, and the #Flyers weren't happy. — Sportsnet (@Sportsnet) April 5, 2015