A member of a team who is considered the primary substitute for a player who plays the majority of the time. The backup will play sparingly, but must be ready to enter the game in the event of fatigue or an injury to the primary player. Backups will also help coach from the sideline, assist in practice, and must have enough of a working knowledge of a position to be able to contribute effectively should they be tasked with entering the game.
Backups are an important part of a football team given the fierce nature of the sport. Since injuries are probable, a team will try and maintain a roster of capable backups who can enter the game in the event of an injury and contribute at a level near the effectiveness of the starter. Backups are also useful during practice as a second team for the starters to scrimmage against. Backups can also help keep a starter fresh by playing a few plays a game so the start can come out of the game and get a break.