Game 1 of the NHL Eastern Conference final featured Pittsburgh Penguins captain Sidney Crosby jawing with Boston Bruins captain Zdeno Chara.

Now we may know why.

During a scrum in the dying seconds of the second period, Chara apparently delivered a blow square to Crosby’s injured jaw while the Penguins star was being held by Bruins centre Patrice Bergeron.

The Penguins provided TSN with footage of Chara punching Crosby, claiming it to be from Game 1.

Asked about the punch and shown the footage by TSN, Chara denied the incident, emphasizing he wasn’t penalized on the play.

The clip wasn’t played during TV broadcasts of the game, but Crosby and the Penguins were clearly irate after the scrum. Once the horn sounded, Crosby had words with Chara and Bruins goalie Tuukka Rask, while teammate Evgeni Malkin fought Bergeron.

Crosby missed the last 12 games of the lockout-shortened season and Pittsburgh’s first playoff game with a broken jaw after taking a puck to the face March 30 against the New York Islanders. He wore a protective shield around his jaw for the majority of the playoffs before removing it for the East final.

Below is NBC's broadcast of the final seconds of the second period in Game 1 of the Eastern Conference final.