In ice hockey, play is said to be offside if a player on the attacking team enters the attacking zone before the puck. When an offsides violation occurs, the linesman blows play dead, and a faceoff is conducted in the neutral zone.

There are two determining factors in an offsides violation:

1. Attacking players' skate position. If a player's skate is in contact with the blue line, he is considered to be in the neutral zone, thus, the play is not offsides.
2. Puck position. The puck must completely cross the blue line to be considered inside the attacking zone. Once in the zone, it must completely cross the blue line again to be considered out of the zone.

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

• With immediate offsides, play is dead the instant an offsides violation occurs. (Used in USA Hockey youth leagues)
• Delayed offsides 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. (Used in the NHL)
• Tag-up offsides gives the attacking team a chance to get back onside, enter the zone, and attempt to regain control of the puck. For the offside to be washed out (canceled), all players on the attacking team must make skate contact with the neutral zone or blue line for one instant. (Used in Hockey Canada, the IIHF, USA Hockey junior leagues, some North American professional leagues, and adult leagues)

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.

See also: Offside pass (ice hockey)