As we can see, Brendan Gallagher made solid contact with Johnathan Kovacevic. It could have been extremely dangerous, as Kovacevic fell badly on the ice. With three defensemen already sidelined for the Canadiens, losing a fourth would have been dramatic.
Moreover, upon closer examination of the scene, we can even see that the defender's skate dangerously approached Gallagher's face. It could have been catastrophic.
However, that's not the only thing that caught attention. Reviewing the images, we can also notice odd behavior from Cole Caufield and Christian Dvorak towards the end of the video. Their actions sparked numerous reactions on social media.
In the context of the team's recent performance, with eight losses in their last ten games, the reaction of the two players towards Gallagher seems to cast doubt on the harmony in the locker room.
It's also possible that this was just a benign act and the players laughed it off afterward, but it's primarily the dangerous scene of the collision between Gallagher and Kovacevic that has caught our attention.