A penalty given to a player who hits or checks a defenseless opponent into the boards. Depending on the severity of the collision between the opponent and the boards and whether or not an injury occurred, a player can be assessed a minor, major, or match penalty for boarding, and can be subject to further fines and/or suspensions.
If a player checks an opponent who had put themselves in a vulnerable position just before the contact occurs, the player may not be assessed a boarding penalty because their opponent put themselves in a position to be hit immediately before the contact occurred, making the contact unavoidable. Otherwise, a player who has time to see that their opponent is in a vulnerable position should minimize contact, or else a boarding penalty could be assessed. It is up to the referee on the ice to judge if the contact was avoidable or if one player put themselves in a vulnerable position before assessing a boarding penalty.
Furthermore, any unnecessary contact that occurs between two players chasing the puck in a potential icing situation may result in the assessment of a boarding penalty should one of the players impact the boards. If no contact with the boards occurs in this situation, a charging penalty may be assessed.