In the dying minutes of Satuday's Colorado Avalanche win over the Dallas Stars, Avs forward Blake Comeau delivered a sucker punch to the head of Stars winger Antoine Roussel after a scrum had been broken up by the linesmen.
Rouseel, whose arms were being held by the linesmen when the punch was thrown and who had used his far hand to remove his helmet immediately prior, was knocked to the ice by the gloved punch. He got to his feet and off the ice without assistance.
Here's the visual evidence of the punch, from the wonderful Steph.
Now, would any hockey player try to take the extra shot at Roussel if given half a chance? Sure. Is the punch particularly hard? It's a jab, not a roundhouse, but it's forceful enough, especially when it's delivered to the side of the head and immediately the removal of the helmet (which would have absorbed some of the impact).
What this definitely is, though, is nearly identical to the sucker punch that got Jordan Nolan suspended for a game back in March of 2014. Both players who were hit have their arms tied up by the linesmen, and as no punches are being thrown, both Roussel and Jesse Joensuu have every reason to believe the scrum is over. As Patrick Burke said in the Nolan video, "it is perfectly reasonable for Joensuu to expect that he will not be punched in this situation."
Given that the situations are nearly identical and that Comeau, like Nolan, has a disciplinary history (Nolan for cross-checking, Comeau for boarding), a game off would seem like a reasonable discipline in this case.
Another option would be a maximum fine, which Roussel himself received for a similar incident last season. Roussel didn't have a disciplinary history at the time, though, and Comeau does.
Regardless, this is exactly the type of sucker punch the NHL has made clear will not be tolerated in scrums.