A LINEMAN is a position in American football that plays on the offensive or defensive line. The job of a LINEMAN is to block or tackle opposing players, depending on whether they are playing offense or defense. Tackle or guard is a term used to describe two different positions within the LINEMAN position. Tackle is an offensive position that is responsible for blocking the defensive players and protecting the quarterback. Guard is a defensive position that is responsible for tackling the offensive players and disrupting the quarterback's play.