The term 'blue line' is used in which sport?

In ice hockey, two blue lines are painted across the rink. They divide the ice into three zones: the defending zone, the neutral zone in the middle, and the attacking (offensive) zone.

Lines on an ice hockey rink:

Blue lines: two lines, each about 30 cm (12 inches) wide, placed about 64 feet (19.5 m) from each goal line in the NHL. They are mainly used to judge offside.

Red centre line: divides the rink into two halves.

Goal lines: thin red lines at each end, where the goals stand.

Faceoff circles and spots: where play is restarted.

The offside rule:

An attacking player is offside if he enters the opponent's zone (crosses the blue line) before the puck does. When this happens, play is stopped and restarted with a faceoff in the neutral zone.

Icing: if a player shoots the puck from his own half across the opponent's goal line without it being touched, "icing" is called, and the faceoff takes place in the offending team's defending zone.

Other ice hockey facts:

• Each team has 6 players on the ice: 5 skaters (usually 3 forwards and 2 defencemen) and a goalkeeper (goaltender).
• A game consists of three periods of 20 minutes each.
• It is played with a hard rubber disc called a "puck", which is about 3 inches (7.6 cm) in diameter.
• Players can be sent to the "penalty box" for fouls, leaving their team short-handed (a "power play" for the other team).

Ice hockey originated in Canada in the 19th century. The first organised indoor game was played in Montreal in 1875. It is Canada's official national winter sport.

The National Hockey League (NHL) is the top professional league; its championship trophy is the Stanley Cup.

Ice hockey has been an Olympic sport since 1920 (summer) and in the Winter Olympics since 1924.

Why not the other options?

• ✗Field hockey has the 23-metre lines and the shooting circle, not blue lines.
• ✗Squash has terms such as "tin", "service line" and "let".
• ✗Swimming uses lane ropes and a "T" mark at the end of each lane.