The offensive line consists of:     The six backs and receivers are those that line up outside or behind the offensive line. There are four main positions in this set of players:      Depending on the style of offense the coaches have designed, the game situation, and the relative skill sets of the players, teams may run formations which contain any number of running backs, wide receivers, and tight ends, so long as the mandated "four backs and seven on the line" rule is followed. For many years, the standard set consisted of the quarterback, two running backs (a tailback/halfback and a fullback), two wide receivers (a flanker and a split end) and a tight end. Modern teams show a wide variety of formations, from a "full house" formation with three running backs, two tight ends, and no wide receivers, to "spread" formations featuring four or five wide receivers, sometimes without any running backs. The defensive team or defense is the team that begins a play from scrimmage not in possession of the ball. The objective of the defensive team is to prevent the other team from scoring, and win possession of the ball for their side. The defense accomplishes this by forcing the offense to turn the ball over, either by: preventing them from achieving a first down and thus forcing them to punt, forcing the offense to fumble or throw an interception, or, more rarely, forcing a turnover on downs. Unlike the offensive team, the rules of the sport do not restrict the defensive team into certain positions. A defensive player may line up anywhere on his side of the line of scrimmage and perform any legal action. Over time, however, defensive roles have become defined into three main sets of players, and several individual positions. Like their offensive counterparts, defensive linemen (also called rushers) line up directly on the line of scrimmage, close to the ball. There are two positions usually considered part of the defensive line:    Often, a defensive lineman will have their hands on the ground, in a three- or four-point stance before the ball is snapped; this distinguishes their pre-snap stance from a linebacker, who begins in a two-point stance (i.e. without a hand touching the ground). Linebackers play behind the defensive line and perform various duties depending on the situation, including rushing the passer, covering receivers, and defending against the run. Defensive backs, also known as the "secondary", play either behind the linebackers or set to the outside, near the sidelines.