I think it's clean too. Sucks to see that happen, but you can't be looking at the puck like that in the middle of the ice.
Slowing it down from the camera angle that runs along Dal Cole's frontal plane (0:56), the point of contact is the high center of Dal Cole's chest, and the head is going to snap back as a result, making it look like his head was hit. It's still very dangerous as that can cause injury to the neck and spine.
But as far as hockey rules go it's a clean hit.
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