Quoting the Chicago Tribune's Chris Hine...

Hawks defenseman Niklas Hjalmarsson received a match penalty for a shoulder to helmet hit he delivered on Blues winger Ty Rattie in the third period. Hjalmarsson is suspended for Sunday’s game against the Red Wings, a game he was unlikely to play anyway, and could face more discipline pending further review of the hit from the NHL’s Department of Player Safety.

And the Blues' Twitter account: