In ice hockey, a play is offside if a player on the attacking team enters the offensive zone before the puck, unless the puck is sent or carried there by a defending player. When an offside violation occurs, a linesman will stop play. A faceoff is then held at a neutral ice spot closest to the infraction to restart play. In the event the puck carrier's feet cross the blue line while the puck remains outside the blue line, the attacking team's players can enter the zone and be considered onside.
The National Hockey League (NHL) and International Ice Hockey Federation (IIHF) apply similar rules for determining offside. A player is judged to be offside if both of their skates completely cross the blue line dividing their offensive zone from the neutral zone before the puck makes contact with the same line. In both organizations, it is the position of a player's skates that are important. They cannot use their stick or other part of their body to remain onside. The lone caveat to this rule is that an attacking player's skates may precede the puck into the attacking zone when they are skating backwards and if they are in control of the puck.
If any individual player is in an offside position, their entire team is offside. A delayed offside occurs if the puck is passed or shot into the offensive zone while an attacking player is offside but has not been touched by a member of the attacking team. In most leagues, the attacking team may "tag up" by having all players exit the offensive zone. At that point the offside is waved off and they may re-enter the offensive zone in pursuit of the puck. If a member of the attacking team has control of the puck while offside, a linesman will stop play and a faceoff will be held at the faceoff spot nearest the point of the infraction. Typically, this means the spot closest to the blue line if the puck is carried into the zone, or in the case of a pass, the spot closest to where the pass originated. If a linesman judges that the attacking team acted to force a deliberate stoppage in play by going offside, they can move the faceoff into that team's defensive zone. At some levels, such as younger divisions of minor hockey sanctioned by USA Hockey, the delayed offside rule is replaced by the immediate offside rule in which the linesman will stop play as soon as a play goes offside, regardless of whether or not the attacking team is in possession of the puck.
Under both NHL (Rules 83.1 and 83.2) and IIHF (Rule 7) rules, there is one condition (two under NHL rules) under which an offside can be waved off even with players in the attacking zone ahead of the puck.
During a faceoff, a player may be judged to be in an offside position if they are lined up within 15 feet of the centres before the puck is dropped. This may result in a faceoff violation, at which point the official dropping the puck will wave the centre out of the faceoff spot and require that another player take their place. If one team commits two violations during the same attempt to restart play, it will be assessed a minor penalty for delay of game.
An offside pass (or two-line pass) occurs when a pass from inside a team's defending zone crosses the red line. When such a pass occurs, play is stopped and a faceoff is conducted in the defending zone of the team that committed the infraction.
There are two determining factors in an offside pass violation:
This offside pass rule is not observed by all leagues. For instance, it was abolished by the IIHF, and its member countries' leagues (except the NHL) in 1998. The National Hockey League adopted the version used by the top minor leagues, under the terms of their 2005 Collective Bargaining Agreement, in which the centre line is no longer used to determine a two-line pass. This was one of a number of rule changes intended to open up the game and improve scoring chances, making the game more exciting for the fans.
In the sport's earliest history, hockey was played similar to rugby in which forward passing was not allowed at any time. Also the hockey's offside penalty was influenced from the offside penalty from Association football. A legal pass could be made only to a teammate who was in an "onside" position behind the puck, thus forcing players to skate with the puck to move it forward. In the event of an offside pass, the play was stopped and a faceoff conducted from the point of the infraction, regardless of where it occurred. The first significant relaxation of this rule occurred in 1905 when the Ontario Hockey Association began to allow defensive players to play the puck within three feet of their goal if the puck rebounded off the goaltender. In some cases, a black line was painted onto the ice surface at that three foot mark and served as an early precursor to the modern blue lines.
Forward passing within the neutral and defensive zones was first allowed in the NHL in 1927 but after a season of extremely low scoring in 1928-29, the league first allowed forward passing in all zones. The result was immediate and dramatic as the number of goals scored per game more than doubled immediately. Under the NHL's new rule, there were no restrictions placed on where a player could be relative to the puck, resulting in players standing deep in their offensive zone while waiting for teammates to bring the puck forward. As a result, the NHL introduced the modern offside rule requiring that the puck precede attacking players on December 16, 1929, and which took effect six days later.