, former Dallas Cowboys quarterback, throwing the football.
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
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
. 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
 or it could be an effort to avoid being
sacked by the defense.
quarterback Craig Candeto pitches the ball while running an option-based offense.
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
requires quarterbacks to throw the ball in most plays.
 The passing game is emphasized heavily in the
(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
(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.
In the NFL, quarterbacks are required to wear a
between 1 and 19.
 In the
National Collegiate Athletic Association (NCAA) and
National Federation of State High School Associations (NFHS), quarterbacks are required to wear a uniform number between 1 and 49; in the NFHS, the quarterback can also wear a number between 80 and 89.
 In the CFL, the quarterback can wear any number from 0 to 49 and 70 to 99.
 Because of their numbering, quarterbacks are
eligible receivers in the NCAA, NFHS, and CFL;
 in the NFL, quarterbacks are eligible receivers if they are not lined up directly under center.