Unlike other sports, hockey teams split their players into offensive lines, and defensive pairs. In order to play more efficiently and guarantee a higher success rate, coaches separate their players into different groups based on their dynamic on and off the ice. This is typically done based on each individual's strengths and weaknesses as a hockey player. Hockey players typically only stay on the ice for 45 seconds at a time in order to keep their stamina as consistent as possible throughout the entire game. This means that players are changing on and off the ice constantly. To do this as efficiently as possible, each player only changes with players of the same position.
This system's main goal besides efficiency is in regards to avoiding an extra person penalty. Because only five players and a goalie per team are allowed on the ice at a time, by matching up with other players of the same position, it is much easier to track how many players are on the ice at one time, and that there are no more than the maximum amount.
In terms of offensive lines in hockey, these lines are made up of three offensive players, called linemates. Each line consists of two wings, a left and a right, and one center player. One example of an offensive line change is that the center player will only change on and off of the ice with other center players, specifically the center on the ice before them. In order for a hockey line change to be completed efficiently, all three positions must be filled by new players, meaning that all three members of one line will switch with all three players of another forward line.
For defensive players, the same concept applies, however instead of three players switching on and off of the ice, only two players will be switching. For a defenseman, only pairs of two players will change each time. Defensive pairs are made up of a left defenseman and a right defenseman, therefore for each defensive line change, the right defenseman will only change with the right defenseman on the ice before them.
In ice hockey, players are allowed to make substitutions with other players as frequently as they, or their coach, would like. In hockey specifically, line changes are made typically every 45 seconds or so, depending on what is going on in the game at the time. The time period that a player, or line, is out on the ice for is referred to as a "shift". Shifts in hockey are very short because the combination of the physical skating requirements and the fast pace of the game make ice hockey one of the most tiring sports.
The blue lines in hockey are used to designate where the offensive/defensive zones for each team are located. There are two blue lines on every ice surface, and each line is located approximately 25 feet away on adjacent sides of the center red line. These are very important lines because they are also used to call offsides, a stoppage of play that is crucial to the fairness of the game.
Because hockey is played in an ice rink and on an ice surface rather than a field or court, a special hockey bench is used by teams each game. Hockey rinks are made by surrounding the ice surface with special boards that are at minimum 3.3 feet tall. Benches are made for both teams with two doors that open up these boards. One door is for the defensive players, and the other is for the offensive players. When players are changing during game play, many jump over the boards instead of using the doors, because it is much faster.