That having been said, this seems to be a bit of an extenuating circumstance.
Duncan Keith's glove came off in the course of regular play, and as he bent over to pick it up, Jeff Carter hit it with his stick. That may or may not have been intentional, and it may or may not have been just agitative, or perhaps malicious.
In response, Keith took his stick and gave Carter a whack. Unfortunately, it hit Carter right in the face.
Keith apologized immediately, which would imply that he in no way intended to hit Carter there, only that he meant to give him a tap on the arm or something in response to Carter trying to hit Keith's glove away from him.
He then apologized again after his penalty was over. I'm not saying an apology wipes out anything that anyone has ever done wrong, but most players don't apologize that quickly and more than once if they actually had malicious intent.
Keith's comments after the game:
Now, the NHL is looking into it, and there's a chance that Keith could be facing a suspension or a fine. What do you think? Should he be punished for this? Or should the league just let it slide?
Hat tip to Puck Daddy for the video