One of the most difficult things to understand for new hockey fans is just exactly how and why the players make substitutions so frequently and sometimes at seemingly random intervals. In most sports players either wait on the bench or on the sidelines until a stoppage in play allows for a substitution. In hockey, this does happen but players also change “on the fly” during the course of the game. Why? Look no further, we’ve got you covered.

Hockey is an anaerobic sport as opposed to an aerobic sport, meaning that it’s played in short, fast and intense intervals. In other words, it’s a sprint not a marathon. This is why hockey shifts are so short.

Hockey is a fast sport, sometimes it’s even referred to as the fastest sport on Earth. The puck moves fast, the players move fast and, as a result, the game moves fast.

Short bursts of energy

New fans or casual viewers of hockey sometimes have a hard time understanding why the players make substitutions so frequently. Afterall, basketball players, baseball players, soccer players and athletes in other sports can play the entire game with needing substitutions.

The biggest difference between hockey and those sports is that hockey is played in short bursts of energy, as opposed to longer, more drawn out stints.

“People really have the hardest time understanding how long a shift is, and it’s only about 45 seconds,” former NHL player Murray Craven explains for the Las Vegas Sun. “People say, ‘What do you mean 45 seconds? That’s all?’ I tell them, ‘It’s a 45-second sprint, so just go out your front door and run down the block as hard as you can for 45 seconds and see how tired you are.”

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

Who goes where?

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 really, substitutions are made by players 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 him or her.

Hockey lineups consist of a forward group (right wing, center, left wing) and a defensive group (two defensemen, one goaltender). Typically individual substitutions will be made on the fly, while 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.

This is what happens when line changes are badly timed – timing and speed is key.

Too many men on the ice

If a team gets too loose with substitutions or line changes made on the fly then they’re at risk of earning a “too many men on the ice” penalty from the referees. Any player exiting the playing surface during the course of play must be within five feet of their bench before their replacement can enter the playing surface.

If either player enters touches the puck or interferes with the play in any way before the substitution is completed then they’ll incur a two-minute minor penalty.

Ice time

While hockey players play such short shifts, the shifts add up over the course of a 60 minute game with the top players sometimes playing more than half the game.

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

Goaltenders typically play the entire game.

The top 42 players by ice time for the 2018-19 NHL regular season were all defensemen. In fact, just two forwards cracked the top 50 for ice time.

Minnesota Wild defenseman Ryan Suter, Los Angeles Kings defenseman Drew Doughty and Pittsburgh Penguins defenseman Kris Letang all averaged more than 26 minutes per game over the league’s 82 game regular season schedule.

Meanwhile, the top three forwards in ice time were Connor McDavid and Leon Draisaitl of the Edmonton Oilers and Patrick Kane of the Chicago Blackhawks, whom all averaged just over 22 minutes per game.

Get on, get off

In summary, hockey is an extremely demanding sport that requires players to be at their absolute best. When you’re tired, you’re more prone to make mistakes or simply slow down.

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