The blue lines on a hockey rink can be confusing to people new to the sport. It’s best to think of them as dividing lines for the different “zones” of the rink. If the home team is defending the net on the right hand side of the rink, then the home team’s “defensive zone” would be from the right side’s blue line back to the boards. The area between the blue lines is called the “neutral zone.”
The blue lines dictate the pace of play in several different ways. Coaches and players use the blue lines as part of their strategy, and as a way to slow the game down from time to time.
The most common purpose of a blue line is to make sure that the offensive team does not enter the opposing team’s defensive zone illegally. As the offensive team makes its way towards the opposing team’s net, they must be sure that the entire puck has crossed the entire width of the blue line before any offensive player enters the zone.
For an offensive player to be offsides, both of their skates must cross the blue line before the puck does. If only one skate crosses the blue line before the puck, then the player is still onsides.
If the offensive team is attacking in the defensive zone and the puck completely crosses back over the blue line into the neutral zone, then all of the offensive players must skate out of the defensive zone before the puck can be brought back in.
Blue lines don’t just limit players’ movements on the ice, though. They also limit where a player can send the puck thanks to the “icing” rule. Icing occurs when an offensive player is on their own side of the center red line and shoots the puck across both the defensive blue line and across the defensive goal line.
The blue line also serves a few other functions. In most leagues, a goalie is not allowed to carry the puck past their own blue line. Some leagues have an infraction called a two-line pass which occurs when an offensive player starts a pass inside their own zone and completes that pass to another offensive player on the defensive side of the red line. The NHL has eliminated this rule, but it still exists in some leagues.
The blue lines in hockey are the core of how the game flows. Once you understand the blue lines, you are on your way to understanding the main rules of hockey.