Change Agents

Chaotic. Confusing. Fast-paced. A work of art. All terms to describe line changes in hockey, which in turn differentiates the game among the world's most popular sports.
A line change is substituting players on the ice for players on the bench during the flow of a game with the clock running and action not stopping. Even though the concept may seem simple enough, it's not always so black and white; there can be gray area.

To an NHLer, or anyone who has played some form of competitive hockey, the line change, or "changing on the fly" or "changing" is a routine as shooting or passing. Players are on the ice for an average of 30 to 45 seconds at a time in the NHL and other high-competition leagues. But those "shifts "can extend to the 60 -or even 90- second range.
Once a shift is over, the players head to the bench, relieved by the next teammates up. Coaches orchestrate the line changes in groups: three forwards on a formed "line" and two defenders who play together as a pair. Those lines and pairs will play together across multiple games and practices. But Kraken fans will discover some coaches like to mix up lines and even defensive pairs during play, especially depending on game situations (leading or trailing by a goal, a player looks off, man-advantage powerplay).

In some cases, lines and pairs will play together for an entire season or multiple seasons (such as the "Grind Line" in Detroit in the late '90s). Those linemates have certain familiarity with one another. They know where each other will be on the ice, know one another's tendencies, strengths and weaknesses, where and when a pass will be.
But how do players know when it's time to change? Enter the gray area. Sometimes a coach will call for a change from the bench, making the decision an easy one. Other times, player intuition leads to the change.
A 30- to 45-second shift does not seem like a long time-until you take into account the fast nature of the sport and that a player is constantly moving, chasing, dodging and, essentially, sprinting for the entirety of that time. It is not hard to empty the tank in practically no time at all. At the end of a game, your top players can average 25 minutes or more of ice time. Players can sense this, so when they feel that fatigue at the end of a shift, they know it is time signal the bench to get ready to change, get the puck into the defensive zone and get off the ice.
There are situations where the opposing team will dictate which line your team puts out onto the ice. Hockey is a game of matchups. The top two lines are responsible for the bulk of scoring, while the third line tends to be in charge of providing energy and shutting down the top two scoring lines. The fourth line in top leagues are commonly known as the tough checking line. In pregame meetings or film sessions, a coach might look at the third line and say, "whenever their top line gets onto the ice, you guys are up!" So even if your team's scoring line just came over the boards, strategy or momentum may dictate a quick shift for them in order to get your shutdown line back onto the ice.

There are many do's and don'ts when it comes to changing on the fly. A player needs to know who they are changing for, and communication is key. Discussing with teammates on different lines in between plays or before a game can mean the difference between a perfectly executed line change or a blown assignment resulting in a goal against.
When players numbers are called to get to the bench for a change, they have to make sure they get off the ice quickly. The game moves fast. When a change is called, and two of your line mates get off and you are still out there for an extended period of time, it can affects strategy and can lead to mismatches.
Since it is not a good idea during live action to have all three of your players change at the exact same time, there will be some overlap. But that overlap should last a few seconds at the most. What is worse, is if the third member of that line comes over the boards and the last line is not completely off, your team may be called for a too-many-men-on-the-ice penalty, giving the opponents two precious minutes of play with your team shorthanded.
There are plenty of situations when it simply is not advantageous to change. Some of these include when your team is on a three-on-one rush, when your team is on a two-on-two move toward the opposing goal, or changing when the other team has control of the puck, especially in your team's defensive zone. There will be times when teams cannot execute a full change, say a player gets trapped on the ice defending against an opponent's extended attack, or your team is looking to take advantage of the other team's fatigued unit. The solution is to substitute one or two players at a time. While appropriate in moderation, it should not become a habit.
At the end of the day, line changes are a chaotic, potentially confusing, sometimes funny and, most importantly, necessary to the game of hockey. Done properly, and your team, and in particular your favorite line or defensive pair (maybe you play on it!), will be on the ice a lot to score goals and win games.