"It's not boarding when the player is against the boards and is checked but glad you have no clue".
Hmm, couldn't seem to find that language in the definition...
Rule 603 | Boarding
(Note) Boarding is the action where a player pushes, trips or body checks an opponent causing them to go dangerously into the boards. This includes: Accelerating through the check to a player who is in a vulnerable position, driving an opponent excessively into the boards with no focus on or intent to play the puck, or any check delivered for the purpose of punishment or intimidation that causes the opponent to go unnecessarily and excessively into the boards.
The onus is on the player delivering the check to avoid placing a vulnerable or defenseless opponent in danger.
(a) A minor plus a misconduct or major plus game misconduct penalty shall be assessed for boarding an opponent.
“Rolling” an opponent along the boards where he is attempting to go through too small an opening is not considered boarding.
(b) A major penalty plus game misconduct penalty shall be assessed to any player who injures an opponent as a result of boarding.
(c) A match penalty for attempt to injure or deliberate injury to an opponent may also be assessed for boarding.