Tough call. Norsen has the right to pursuit the puck and Tage Thompson just happened to be in same vicinity
He was fishing for the puck and made the pass and just happened to hit him. He was bracing for the collusion after making the pass. I think the rules needs some tinkering. Hits like this when he made play don't deserve a major hit but the problem is that the rulebook doesn't allow for the flexibility and the league need to amend the rulebook concerning the hit to allow for grace between collusion after making the pass and brace for hit to protect himself. I think that 2 seconds after the pass should be enough to make it a penalty. If it's 1 second after the pass and collusion to any part of the body shouldn't be a penalty.
According to the rulebook, it's a major hit without the amendment to the rulebook. Hopefully that the NHL address this amendment to the illegal check to the head collusion with no penalty if there is a play made with the puck and reverse hit happened for the off-season discussion with the league rules committee. If they had this in the rulebook, this very Norsen hit will be made legal without a major penalty.; Just like the high-sticking penalty, the league has made amendment to high-sticking after the follow-through to ensure that it is not a high-sticking penalty for example.
So in other word, let's use that video as an example to amend illegal check to the head rules since he had made the play with the puck which is within his right to do it so. It is an unfortunately situation.