The play in question occurred late in the second period. As Senators defenseman Cody Ceci played the puck behind the net off a feed from Jared Cowen, Nazem Kadri lined him up and hammered him from behind. Kadri then backhanded the puck out front to Joffrey Lupul, who tied the game with a goal.
Of course, the Senators immediately expressed their displeasure by roughing up Kadri.
The Senators wanted a boarding call, but none came. Whether you think it was a dirty play or legal check probably depends on which Ontario hockey team you cheer for.