What is icing in hockey?

Icing is called when a player shoots the puck from behind the center red line across the opponent's goal line and it is untouched along the way. The whistle blows and the faceoff comes all the way back into the offending team's defensive zone, and the offending team cannot change lines, which means tired players stay on the ice against fresh opponents. The rule exists to prevent a team under pressure from simply firing the puck the length of the rink over and over to reset play, which would make the game unwatchable.

Two conditions cancel it. A team that is shorthanded during a penalty is permitted to ice the puck freely, which is why penalty killers can clear their zone without consequence and why power plays involve so much chasing. And icing is waved off if the officials judge the defending team could have played the puck, or if the goaltender leaves the crease to play it. The more consequential change came in how icing is whistled: leagues moved from touch icing, which required a defender to reach the puck first and produced high-speed races into the end boards that broke legs and ended careers, to hybrid or no-touch rules that judge the race at the faceoff dots and blow it dead before the collision.