Zach Sanford of the St. Louis Blues had a hard time getting up after a dirty hit sent him headfirst into the boards. He appeared to be momentarily knocked out before getting back to his skates and needing some help getting off of the ice.
Going headfirst into the boards is almost always going to result in a head injury or worse. You just can't dish out that kind of hit from behind. This is how you give someone a concussion and a bad few days.
It's also how players become paralyzed. There are some who enjoy concussions, but nobody wants to see a play end in paralysis.