In ice hockey, a play is offside if a player on the attacking team enters the offensive zone before the puck itself does, and then receives possession of the puck from the neutral zone. Simply put, the puck must not enter the attacking zone after attacking players. If a player on the attacking team is in the offensive zone before the puck, either an immediate offside occurs, or they must retreat to the neutral zone. For determining offside, the position of the puck and players must be considered to be in the neutral or offensive zone. Usually, the puck enters or leaves the offensive zone when it completely crosses the blue line. A player is in the neutral zone if either skate is in the neutral zone or touches the imaginary plane extending upwards from the leading edge of the blue line; otherwise, he is in the offensive zone. When an offside violation occurs, a linesman will stop play. To restart play, a faceoff is then held at the ice spot closest to the infraction, usually a neutral spot, or if there is a delayed penalty, at a spot in the defending zone of the defending team, which incurred the penalty. Even if the linesman erred in calling offside, the faceoff will still occur. Rules Delayed offside rule Under the delayed offside rule, an infraction occurs when a play is offside and any attacking player touches the puck or checks a player in the offensive zone. For example, under NHL's delayed offside rule, play is stopped immediately when an attacking player carries the puck into the zone while a teammate is already in the attacking zone, or when an attacking player in the neutral zone completes a pass to a teammate who is already in the attacking zone. A delayed offside occurs when a player on the attacking team is in the offensive zone before the puck and the attacking team causes the puck to enter the zone without the attacking team having possession. When a delayed offside occurs, a linesman will keep an arm up to signal it, and all attacking players must retreat back into the neutral zone without touching the puck or checking an opponent for the delayed offside to end. If an attacking player touches the puck during the delayed offside, play is stopped. The National Hockey League (NHL) and International Ice Hockey Federation (IIHF) apply