The position of the primary player who runs the ball for most offenses. Often referred to as the "tailback".
In most offensive systems the halfback lines up several yards behind the quarterback before the play. Once the play begins, the halfback's main responsibility is running the football on plays where the ball is handed off. If it is a passing play, the halfback is often asked to help block or catch passes. Famous halfbacks include Walter Payton, Barry Sanders, Emmitt Smith, and Adrian Peterson.