Here's the suspension video and explanation from the NHL Department of Player Safety:
Ference is a top-four defenseman for the Bruins, so his suspension will require some adjustments to their roster. He played nearly 20 minutes in Game 1, recording three shots, two hits and two blocked shots. This is his second career suspension.
Despite the elbow to the head, Grabovski didn't miss any shifts in the game. If he had suffered a significant injury it might have resulted in a longer suspension for Ference.
The Bruins won the first game of the series 4-1.