A substitute is a player who does not start playing a match on the pitch but is ready to replace a team-mate during the game. Most managers have players that can play in more than one position because, in most matches, only 7 or 5 substitutes can be selected for the match and only 3 can be used. In most situations, a goalkeeper is chosen as one of the substitutes; if the goalkeeper is injured, only another goalkeeper can effectively replace him.
There are a variety of reasons why a substitution may be made.
Injury and RestEdit
If a player becomes injured or his condition drops below a desirable level, the manager may choose to substitute him for a more fit player who will be capable of playing the remainder of a match. If a player is injured so badly that he cannot continue, the manager is forced to make a substitution. A manager may also choose to substitute an important player during a minor match to conserve his condition for future games.
Some managers will bring on a substitute to change things around tactically and improve their chances of winning the game. If a player is playing badly, a manager may choose to replace him with a player who can do a better job. Sometimes, if a manager wishes to change the formation his team is playing in, he may substitute a player with one who plays in a different position. This enables him to apply a new formation or tactic effectively.
Experience and PracticeEdit
To improve, young players need match experience. If a team has a comfortable lead, the manager may choose to bring off a more experience player for a less experienced player to give them match experience and help them to improve.
Some teams have a player who is very effective at replacing a player during the game and making a big impact. These players are often as good as (or close to) the starting 11; however, they may be inconsistent when starting or have a low fitness level. Generally, these players are attack minded in order to turn the game around and will be slightly different from the other players (they may be a lot faster or more creative).