The incident occurred early in the first period when Borowiecki slipped as he carried the puck around his own net. While Borowiecki tried to regain his footing and control of the puck along the boards, Westgarth made a very dangerous check from behind.
Here's another look. You could make the argument that Westgarth couldn't slow down in time, but that little lunge forward at the end really makes it look intentional.
Borowiecki finally left the ice under his own power and hasn't returned. Westgarth received a minor penalty for hitting from behind.