<P> A quarterback (commonly abbreviated "QB") is a position in American and Canadian football . Quarterbacks are members of the offensive team and line up directly behind the offensive line . In modern American football, the quarterback is usually considered the leader of the offensive team, and is often responsible for calling the play in the huddle . </P> <P> In modern American football, the quarterback is usually the leader of the offense . The quarterback touches the ball on almost every offensive play, and his successes and failures can have a significant impact on the fortunes of his team . Accordingly, the quarterback is among the most glorified and scrutinized positions in team sports . Prior to each play, the quarterback will usually tell the rest of his team which play the team will run . After the team is lined up, the center will pass the ball back to the quarterback (a process called the snap). Usually on a running play, the quarterback will then hand or pitch the ball backwards to a half back or full back . On a passing play, the quarterback is almost always the player responsible for trying to throw the ball downfield to an eligible receiver downfield . Additionally, the quarterback will often run with the ball himself, which could be part of a designed play like the option run or quarterback sneak, or it could be an effort to avoid being sacked by the defense . </P> <P> Depending on the offensive scheme by his team, the quarterback's role can vary . In systems like the triple option the quarterback will only pass the ball a few times per a game, if at all, while the pass - heavy spread offense as run by schools like Texas Tech requires quarterbacks to throw the ball in most plays . The passing game is emphasized heavily in the Canadian Football League (CFL), where there are only three downs as opposed to the four downs used in American football, a larger field of play and an extra eligible receiver . Different skillsets are required of the quarterback in each system - quarterbacks that perform well in a pass - heavy spread offensive system, a popular offensive scheme in the NCAA and NFHS, rarely perform well in the National Football League (NFL), as the fundamentals of the pro-style offense used in the NFL are very different from those in the spread system . while quarterbacks in Canadian football need to be able to throw the ball often and accurately . In general, quarterbacks need to have physical skills such as arm strength, mobility, and quick throwing motion, in addition to intangibles such as competitiveness, leadership, intelligence, and downfield vision . </P>

Who does a quarterback throw the ball to