From the NHL Rule Book: "Should the puck strike the spectator netting at the ends and the corners of the arena, play shall be stopped and the ensuing face-off shall be determined as if the puck went outside the playing area. However, if the puck striking the spectator netting goes unnoticed by the on-ice officials, play shall continue as normal and resulting play with the puck shall be deemed a legitimate play. Players must not stop playing the game until they hear the whistle to do so."
