The Sharks were a little upset with the Blues after Maxim Lapierre's hit on Dan Boyle. So angry that they decided to take their frustration out on the Blues physically. Brenden Morrow was the recipient of a nasty cheap shot from Brent Burns. The guilty party here served just two minutes for his infraction even though the hit was well deserving of a larger sentence. You could make a strong case that Burns' hit on Morrow was just as bad as the one on Boyle, but the punishment usually seems to match the injury (or lack thereof) and not the crime.
Consistency, thy name is NHL officiating.
Morrow was forced to leave the game but later returned for the second period.