One of the most challenging things to understand for new hockey fans is exactly how and why the players make substitutions so frequently and sometimes at seemingly random intervals. 

In most sports, players wait on the bench or the sidelines until a stoppage in play allows for a substitution. This happens in hockey, but players also change "on the fly" during the game. Why? Look no further, we've got you covered.

What is a shift in hockey?

A hockey shift is when a line or player goes onto the ice and plays the game. Hockey "lines" often play with each other on forward and defense. Typically, three forwards take a shift together, and two defensemen take a shift together. Although this can be modified during the game, these lines are often determined before the game starts.

The remaining players sit on the bench and either rest or wait for the coach to tell them their line is next to play a shift.

How long do hockey shifts last?

The average hockey shift in the NHL lasts only 40 to 45 seconds. Hockey is an anaerobic sport instead of an aerobic sport, meaning it's played in short, fast and intense intervals. In other words, it's a sprint not a marathon. This is why the average shift lengths are so short.

Hockey is a fast sport; sometimes, it's called the fastest on Earth. The puck moves fast. The players move fast, and, as a result, the game moves fast.

How do hockey players know when to shift?

A player's body will typically tell them when it's time to shift. However, the coach may also organize shorter shifts for the 4th line over the 1st line, for example. Players will also shift when the situation on the ice is favourable. 

For example, you rarely see a player shift off when the puck is in their defensive zone. Doing so would give a short-term advantage to the other team.

Players also often shift on and off the ice depending on their linemates. For example, if a linemate is injured during play and exits the surface, the coach may decide to change the whole line at a whistle, or that line can change on the fly.

In addition to this, the coach may strategically shift players in and out depending on where faceoffs are or who is on the ice for the other team.

Who decides line changes in hockey?

There will be three main people deciding line changes in hockey—the players themselves, the coach, and in some rare instances, the referees and linesman.

A player may decide to change lines for a multitude of reasons. They could be doing so because they are tired, injured, or have witnessed their linemates change.

Secondly, the coach can decide to change players for multiple reasons. For one, he could be line-matching, meaning he is trying to put a set of players out that would be optimal against the opponents on the ice. Or, he could be looking to shift out players based on someone being good at faceoffs. There are multiple ways a coach could decide to change lines.

And finally, the referees and the linesman can decide whether or not a team can change. This primarily comes from a team icing the puck. If they do, they are not allowed to change, and thus the referees will stand in front of the bench and make sure no substitutions are done.

How often do shifts change in hockey?

With the average NHL shift being 40-45 seconds, this means there will be approximately 26 shift changes during a twenty-minute period. During a game, around 78. 

The theory is that after 45 seconds or so, the human body can't handle the speed and tenacity required to play at the highest level. As a result, a substitution can be made on the fly or during a stoppage in play.

Remember, this number can vary wildly, as top-tier players typically take a little longer shifts. In contrast, fourth-line players will take shorter ones.

New fans or casual hockey viewers sometimes have difficulty understanding why players frequently make substitutions. After all, basketball players, baseball players, soccer players and athletes in other sports can play the entire game without needing substitutions.

The most significant difference between hockey and those sports is that hockey is played in short bursts of energy instead of longer, more drawn-out stints.

What are the rules for a line change in hockey?

NHL teams can make changes while the play runs or during a stoppage, as long as the team does not ice the puck. 

On the fly changes must be made with the player coming off the ice being within 5 feet of the bench. Although this is not always caught, if it is, the team will be assessed a too many men on the ice penalty. In addition, the player coming on the ice cannot touch the puck until the player they are substituting for has entirely left the ice. If they touch the puck, it will be too many men on the ice.

Which team gets the last change in hockey?

The home team in an NHL game also gets what is called "last change", meaning they get additional time to make the last substitutions after the away team makes theirs.

How long do NHL players rest?

This is highly dependent on the player's position. A top-tier defenseman may play 30 minutes during a 60-minute game, meaning they are resting for the additional 30 minutes. 

Defensemen typically play more minutes during a hockey game, as they're limited to three pairings of two players. In contrast, forwards have four lines of three players on the roster.

On the other hand, a fourth-line forward may end up playing 7 or 8 minutes of a 60-minute game, meaning their rest time is more than 40 minutes. Typically higher calibre players and players with more stamina take very short rest periods on the bench before being called upon to return to the ice.

Goaltenders will play the entire game and only rest in between whistles or when the puck is at the opposite end of the play.

What is the longest shift in NHL history?

In December 2022, Jack Hughes of the New Jersey Devils played the longest shift in NHL history at six minutes and two seconds. In fact, during the last 8 minutes of the game, he only spent 30 seconds off the ice.

How do hockey players know who to change off for?

Another question that new hockey fans often have regarding changes and substitutions is, "How do the players know who to replace and where to go?"

The answer is simple. Players make substitutions of the same corresponding position as the player they're replacing. So if a right winger exits the ice for substitution, another right-winger will replace them.

Hockey lineups consist of a forward group (right wing, center, left wing) and a defensive group (two defensemen and one goaltender). Typically individual substitutions will be made on the fly. In contrast, full line changes will be made during a stoppage in play.

I write more about this in my article – how hockey players know when to change lines.

Below is a video that shows what happens when line changes are poorly timed – timing and speed are critical.

Get on, get off

In summary, hockey is a highly demanding sport requiring players to be their best. You're more prone to make mistakes or slow down when you're tired.

You give your opponent a competitive advantage when you make mistakes or slow down. Therefore, hockey teams keep their shifts short to always be at their absolute best.