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A starting lineup in sports is an official list of the set of players who will actively participate in the event when the game begins. The players in the starting lineup are commonly referred to as starters, whereas the others are substitutes or bench players.
The starters are commonly the best players on the team at their respective positions. Consequently, there is often a bit of prestige that is associated with being a starter. This is particularly true in sport with limited substitutions like baseball or soccer. In both baseball and basketball, it is common for players' positions to be denoted by a number as well as by a name. In that instance, the associated number is used as well. If a common abbreviation is known, the abbreviation is listed after the associated number.
In American football since the 1950s, most upper level teams use a three-platoon system, each with its own starting lineup. The starting lineups for offense and defense, each with eleven players, typically get the most attention. The starting lineups are defined as the eleven players who take the first offensive or defensive play from scrimmage of a given game. (An offensive player does not have to be on the team that gets possession first to be considered a starter, nor does a defensive player have to be on the team that does not; the first play from scrimmage after the first change of possession counts as well.) The third platoon, special teams, in modern times is composed mostly of backup and reserve players from the offensive or defensive platoons, with the exception of the placekicker or punter; the players who, for instance, take part in the opening kickoff are typically not considered starters.
Offense: The offensive lineup is heavily restricted by rules that have been adopted over the course of the game's development. Several positions are mandatory and must appear in any lineup, starting or otherwise. Others can be used or unused at the discretion of a team's coach, provided that no more than 11 players are on the field at any given time.
There is some variation; for instance, teams that rely more on passing may not use a fullback and start three wide receivers (typically a flanker, slotback and split end).
Defense: In recent history the 4-3 defense (4 defensive linemen plus 3 linebackers) formation has been standard among college and professional squads. However, the 3-4 (3 defensive linemen plus 4 linebackers) formation is becoming more popular among professional and NCAA Division I teams. Unlike offenses, defenses have no restrictions on positions, and the standard lineups have developed largely through tradition, experimentation, trial and error.
The National Football League counts how many times each player takes the first snap of the game. This statistic reflects offense and defense only, not special teams. (Every game starts with a kickoff, which would be a special teams play.) A player gets credited with only one start if he should happen to be on both the offensive and defensive starting lineups (as has happened several times in recent years with Troy Brown of the New England Patriots, who played both wide receiver and defensive back.) Yet, this is not the official starting lineup. The list of players to start the game is usually determined by the head coach of the franchise and not the league.
In American college football, the official record of the game includes a "Game Participation" chart which shows the starting lineups and the other participants. The starting lineups reflect the two teams' offenses and defenses, not the kickoff teams.
In Australian rules football, a team starts with eighteen players on the field. The traditional positions are as listed below, however in modern football the players are organised into three main groups, forwards, midfielders and defenders, each consisting of between four and eight players. Only four midfielders from each team are allowed to start inside the centre square, the other 14 players can start anywhere on the field.
The starting lineup in baseball comprises either nine or ten players. In the National League of Major League Baseball and the Central League of Nippon Professional Baseball, there are nine players in the starting lineup and all players bat. American League (MLB) and Pacific League (NPB) teams have the option of using a designated hitter (DH) in place of the pitcher in the batting order. The DH does not play when the team is on defense.
In softball, the tenth position is an additional outfielder.
In the NBA, two starting players are traditionally announced as guards, two as forwards and one as a center. However, technically the rules merely stipulate that a starting lineup, along with a list of substitutes, must be indicated at least ten minutes before the game. A captain and optionally a co-captain must also be designated. When pre-game technical fouls are committed, only designated starters can be chosen to shoot any resulting free throws. 
The various positions are not mentioned anywhere in the official NBA rule book, and most players play more than one position.
The starting lineup on a basketball team usually comprises five positions and is called the 2-1-2 lineup:
In American college basketball, a starting lineup is announced for each team before the game. Starting players are designated as either centers, forwards, or guards. A team can name at most one center, but otherwise any combination of positions is allowable, as long as five players are named. Lineups of three guards, one forward, and one center, or of three guards and two forwards, are the most common alternate lineups.
In Canadian football, a team starts with 12 players on offence, 12 players on defence, and a special teams squad of 12 players for punts, kickoffs, and extra point attempts. As in American football, most of the special teams players are starters or bench players for offence or defence.
Because of substantial differences between the two codes—most notably the larger field and only having three downs to advance the ball 10 yards instead of four—offensive formations are somewhat different in the Canadian game. Most notably, tight ends are almost completely absent in Canada.
Defences are broadly similar to those in the U.S., with the extra player used as a defensive back. Since most of the positions are essentially identical to those in American football, only the main differences will be listed here.
Positions generally similar to those in the U.S.
Gaelic football and hurling, as well as ladies' Gaelic football and camogie, use the same starting lineup. Teams consist of one goalkeeper and fourteen outfield players (underage teams may play 13-a-side, omitting the full back and full forward positions). Teams lineup in six lines, with the goalkeeper furthest back and the full-forward line closest to the opposing team's goal. Players play on the left or right of the field looking in the direction they are attacking. Position numbering is fixed and positions are set up so that every attacker has a corresponding defender: for example, a right corner forward (jersey number 13) will be marked by a left corner back (4). Players sometimes swap positions during a match and there are sometimes tactical variations in formation, such as dropping one of the six forwards back to provide a third midfielder. Up to five substitutions are allowed during normal time (and another three if there is extra time), from a bench of 9 or sometimes 11 substitutions; substitutions are not numbered in any particular order.
In ice hockey, a team starts out with six players on the ice:
The starting forwards are typically known as the top line or first line, as most professional teams rotate four distinct three-man forward lines and three defense pairings.
The starting lineup in field lacrosse comprises ten players: 3 Attackmen, 3 Defensemen, 3 Midfielders, and 1 Goalkeeper. A team may start a Long-Stick Midfielder for a defensive advantage. A team may have a player reserved exclusively to take face-offs, known as a FOGO.
In netball, a team starts with seven players on the court:
A Rugby league football starting lineups is
Rugby union starting lineups consist of:
The starting lineup for a volleyball match typically includes:
Variations do exist - sometimes there will be two setters, or three outside hitters without a true opposite. Though the libero is typically announced with the starting lineup, he or she is not considered to be part of it, as the libero will replace one of the above players (typically a middle blocker, as teams will want to split their middle blockers, with one beginning in the front row) before the first rally.