Sidney Crosby has a history of concussions and that's why a play like this makes you immediately concerned about his well being. Off a faceoff with Mika Zibanejad, Crosby appears to take a high stick in the temple. The play wasn't malicious, but it was a clear high stick.
Crosby left the ice with a trainer and has not returned to the bench since. The score is currently 3-3 during the second intermission.
After being hit by the high stick Crosby hit the ice, so he may have been pulled into concussion protocol.
Update: It appears Jacob Trouba may have caught Crosby with an elbow on the same play.