Not enough time to react to them stopping and pulling their head back to make the decision to flare out your elbow and also to act on it...
I'm sorta surprised how quick reaction times people seem to have, Rempe wasn't even looking at the guy's head.
That was just a hit with which he attempted to level the guy against the boards, but then Siegenthaler braked and pulled his upper body back so Rempe missed.
You know who disagrees with you? The NHL DofPS.
Watch the video:
“It is important to note that while we acknowledge that Siegenthaler is stopping up as he is dumping the puck in, this is not a case where a sudden movement by the player receiving the check turns a legal check into an illegal one.”
“We do not believe this is accidental contact as the player is bracing for impact with the boards or another player.”
“Rempe is clearly committed to throwing a check on this play and having ended up at an angle of approach that will take him across the front of Siegenthaler’s body, and potentially miss Siegenthaler entirely, Rempe chooses to flare his elbow both up and away from his body in dangerous fashion, driving it directly into the head of Siegenthaler with substantial force.”
Players learn to not flare their elbows out in order to avoid Elbowing penalties.