I don't have any idea what caused this, but the only way to describe it is disgustingly dirty.
Videos by FanBuzz
The Dakota College at Bottineau Lumberjacks were on their way to defeating The Erie Community College Kats for the NCJAA Hockey Championship when an Erie player came flying out the penalty box and viciously hit a referee. The referee looks like his head bounces off the ice, and he lay motionless. The player was tackled by others.
Here's another view:
https://www.instagram.com/p/BQ_hcqzDsof/?taken-by=barstoolsports
According to Sports Illustrated, the game was in its final minute when the brutal hit occurred, and it was called, giving Dakota College a 7-4 victory.
Since this is a developing situation there are a number of unanswered question, including the identities of the player and referee, why the player was in the penalty box, and whether authorities might get involved. We'll update as more details become available.