I understand he hit him in the head with his shoulder, but at the same time they guy skated directly into him with his head down. Kronwall caught him right on the chin.
It was actually alot like the hit he put on Havlat a while back.
This season there is a rule change about head shots, but read the definition....
http://www.nhl.com/ice/news.htm?id=539622
48.1 Illegal Check to the Head- A lateral or blind side hit to an opponent where the head is targeted and/or the principle point of contact is not permitted.
There is a video to explain...
http://sabres.nhl.com/club/news.htm?id=538073
The video even explains that "North-South hits" are legal and show a guy skating into a check where they guy hits him head on. IMO, that is exactly what Kronwal did. The many examples of illegal hits are lateral or blindside hits to the head.