A very dangerous play where a player bodychecks an opponent from behind, usually into the boards, often resulting in injury and in rare cases paralyzing the opponent. The penalty for checking from behind when a player can't protect himself is an automatic 5 minute major and a game misconduct.
Checking from Behind used to be considered "Boarding" in the rule book and is still used to assess minor penalties for bodychecks delivered from behind where an opponent protects himself before hitting the boards.
Some critics have said an increased awareness to rid the game of "Checking from Behind" plays with strict enforcement has done more harm than good. Some puck carriers are now turning to either draw penalties or get the defensive player to let up a bit.
The National Hockey League - NHL, however, does not penalize players who check a player from behind if that player intentionally turned immediately prior to the hit.