A linebacker (LB or backer) is a playing position in gridiron football. Linebackers are members of the defensive team, and line up approximately three to five yards (4 m) behind the line of scrimmage, behind the defensive linemen, and therefore "back up the line". Linebackers generally align themselves before the ball is snapped by standing upright in a "two-point stance" (as opposed to the defensive linemen, who put one or two hands on the ground for a "three-point stance" or "four-point stance" before the ball is snapped). The goal of the linebacker is to provide either extra run defense or extra pass defense based on the particular defensive play being executed. Another key play of the linebacker position is blitzing. A blitz occurs when a linebacker acts as an extra pass rusher running into any exposed gap. When a blitz is called by the defense, it is mainly to sack or hurry the opposing offense's quarterback. Linebackers are often regarded as the most important position in defense, due to their versatility in providing hard hits on running plays or an additional layer of pass defense, when required. Similar to the "free safety" position, linebackers are required to use their judgment on every snap, to determine their role during that particular play.