As you say, the hit was fine. Matheson used his size and strength advantage to separate Pettersson from the puck and remove him from the play. What happened after was not fine: grabbing the shoulders of a player off balance from the hit and shoving him to the ice back first when he's not in a position to protect himself is a dangerous play, and the outcome (concussion) isn't really surprising. There's room for physical contact, but hockey is not a combat sport. Hopefully the NHL chooses to protect its stars. We'll see how the hearing goes today.