A phrase used to describe the changing of players on the ice while play is live. Unlike many other sports where players must sub in and out of the game when play is stopped, hockey players can head off for a substitute at almost any time of the game.
For the newest of hockey fans, seeing players "change on the fly" in person at their first few games can be incredibly confusing, but it isn't as complicated as it looks. Generally, players on the bench will talk to each other and work out who is going out for each guy.
Players usually decide when they come off the ice, generally when they get tired or feel it won't harm their team defensively. Changing on the Fly makes the game much faster as fresh players are always entering into the game every 30 to 45 seconds.
Substitutes must be careful to wait for teammates coming off the ice to be at least 10 feet away from the bench and not participate in play until the player is back on the bench. Often times, Too Many Men on the Ice penalties occurr because of this impatience on the bench.