A defensive tackle is a position in American football that typically lines up on the line of scrimmage, opposite one of the offensive guards; however, he may also line up opposite one of the offensive tackles. Defensive tackles are typically the largest and strongest of the defensive players. Depending on a team's defensive scheme, a defensive tackle may be called upon to fill several different roles. These may include merely holding the point of attack by refusing to be moved, or penetrating a certain gap between offensive linemen to break up a play in the opponent's backfield. If a defensive tackle reads a pass play, his primary responsibility is to pursue the quarterback, or simply knock the pass down at the line if it is within arm's reach. Other responsibilities of the defensive tackle may be to pursue the screen pass or drop into coverage in a zone blitz scheme. In a traditional 4–3 defense, there is no nose tackle. Instead there are a left and a right defensive tackle. Some teams, especially in the National Football League , have a nose tackle in this scheme, but most of them do not.