Both Erat and Gudbranson were chasing after the puck when the incident occured, but Erat had dished it off to a teammate by the time Gudbranson got into a position where he could make contact with him. As Erat turned, Gudbranson bore down on him and drove him hard into the boards. It looked like Erat was already losing his balance and was low to the ground when Gudbranson shoved him from a higher angle.
At any rate, Erat went head-first into the boards and was clearly shaken up. He left the game and there hasn't been any update on his status. Will Brendan Shanahan give Gudbranson a call tomorrow?