American football positions

In American football, each team has 11 players on the field at one time. The specific role that a player takes on the field is called his position. Under the modern rules of American football, teams are allowed unlimited substitutions; that is, teams may change any number of players after any play. This has resulted in the development of three "platoons" of players: the offense (the team with the ball, which is trying to score), the defense (the team trying to prevent the other team from scoring, and to take the ball from them), and the special teams (who play in kicking situations). Within those platoons, various specific positions exist depending on what each player's main job is.

In American football, the offense is the side in which the players have possession of the ball. It is their job to advance the ball towards the opponent's end zone to score points. Broadly speaking, the eleven players of the offense are broken into two groups: the five offensive linemen, whose primary job is to block, and the six backs and receivers whose primary job is to advance the ball either running with the ball or passing it. The backs and receivers are also commonly known as skill position players or as eligible receivers (or eligible ball carriers). Offensive linemen are not usually eligible to advance the ball past the line of scrimmage during a play.

The organization of the offense is strictly mandated by the rules; there must be at least seven players on the line of scrimmage and no more than four players (known collectively as "backs") behind it. The only players eligible to handle the ball during a normal play are the backs and the two players on the end of the line (the "ends" or Tight ends). The remaining players (known as "interior linemen") are considered "ineligible", and may only block. Within these strictures, however, creative coaches have developed a wide array of offensive formations to take advantage of different player skills and game situations.

The following positions are standard in nearly every game, though different teams will use different arrangements of them.

The offensive line is primarily responsible for blocking. During normal play, offensive linemen do not handle the ball (aside from the snap from center), unless the ball is fumbled by a ball carrier, a pass is deflected and caught by a lineman or when a player who is normally an offensive lineman takes a different position on the field. The offensive line consists of:

...
Wikipedia