Offside

In ice hockey, play is said to be offside if a player on the attacking team enters the attacking zone before the puck itself enters the zone, either carried by a teammate or sent into the attacking zone by an attacking player. If a defending player carries, passes, or otherwise intentionally sends the puck into his defensive zone, any attacking player in the zone is not offside. However, if an attacking player is attempting to shoot the puck into the attacking zone and it deflects off a defending player, an offside violation can still occur. This is unlike the icing rule, where an unintentional deflection by the other team will negate an icing call.

When an offside violation occurs, the linesman blows the play dead, and a faceoff is conducted in the neutral zone closest to where the offside was.

There are two determining factors in an offside violation:
 * 1) Attacking players' skate position:  One of a player's skates is not in contact with or behind the blue line of the attacking zone before the puck enters that zone.
 * 2) Puck position: The puck must completely cross the outer edge of the blue line to be considered inside the attacking zone for the purposes of offsides.

Note that the puck must enter the attacking zone for an offside call to be made; a player being over the line does not result in an offside call until the puck crosses the line, and that a player cannot put himself offside, such as by carrying the puck in while skating backwards.

Note: In the NHL, a player controlling the puck can have his two skates cross the blue line before the puck, and he can then pull the puck in behind him. He must however be in complete control of the puck.

Though the basic offside rule is always the same, there are different rules for the situation when the puck is shot in while a player is offside, but the defending team gains control of the puck.

Tag-up offside is used in NCAA, Hockey Canada, the IIHF, USA Hockey junior leagues, some North American professional leagues, adult leagues, and the NHL from 1986-1996, and once again after the 2005 Collective Bargaining Agreement.
 * With immediate offside, play is dead the instant an offside violation occurs. Immediate offside is used in the USA Hockey youth leagues.
 * Delayed offside allows the defending team a chance to move the puck out of the zone. The play remains offside until the puck enters the neutral zone. Play is blown dead if the defending team does not attempt to move the puck forward. Simple delayed offside was used in the major North American leagues in the AHL until 2004 (except from 1986-96), in the ECHL until 2005 (except from 1996–2005), and in the NHL until 2005 (except from 1986–96).
 * Tag-up offside is a variation of delayed offside. In a delayed offside situation, if all members of the offending team clear the defensive zone at the same time by making skate contact outside of the zone (including the blue line), then the delayed offside call is negated.

Play is stopped immediately if a player from the attacking team touches the puck in the attacking zone while he or any of his teammates is offside.

Offside is also used to refer to a player lining up on his opponent's side during a faceoff. There is no penalty for this, though the faceoff may not be conducted while a player is offside.

Offside pass
In ice hockey, an offside pass or second (blue) line pass is a pass from inside a team's defending zone that 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:
 * 1) Puck position when pass is released. Since the blue line is considered part of the zone the puck is in, if the puck is behind or in contact with the blue line when the pass is released, the pass may be an offside pass.
 * 2) Skate position of the receiver. If the receiver has skate contact with the red line at the instant the puck completely crosses it, the pass is legal regardless of where the puck actually makes contact with his stick. Both of his skates must be completely on the far side of the red line when the puck crosses the red line into the attacking zone is governed by the aforementioned offside rule.

This offside pass rule is not observed by all leagues. It has never been enforced in European league play. The National Hockey League recently adopted the version used by the top minor leagues, under the terms of their 2005 Collective Bargaining Agreement, in which the center 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.