The quarterback (commonly abbreviated "QB"), colloquially known as the "signal caller", is a position in gridiron football. Quarterbacks are members of the offensive platoon and mostly line up directly behind the offensive line. In modern American football, the quarterback is usually considered the leader of the offense, and is often responsible for calling the play in the huddle. The quarterback also touches the ball on almost every offensive play, and is the offensive player that almost always throws forward passes. When the QB is tackled behind the line of scrimmage, it is called a sack.