Quarterback (QB, originally called blocking back) is a position in American and Canadian football. Quarterbacks are members of the offensive team and line up directly behind the offensive line. Quarterbacks are the leaders of the offensive team, responsible for calling the play in the huddle.
At most levels, but especially at the college and professional level, the quarterback role is the most visible and important role on the team. The quarterback touches the ball on nearly every offensive play and has a great deal of responsibility both in calling plays and making decisions during the play.
In most leagues, the quarterback's uniform number is as low as 1 and as high as 19. It is extremely rare that a quarterback has a number over 19.
While there is liberal substitution at most positions in football based on the play call and to minimize player fatigue, most quarterbacks are on the field for every offensive play leaving only for injury or when the game's outcome is no longer in doubt. Quarterbacks are frequently chosen early in the NFL Draft and often receive much more lucrative contracts than other positions. As of 2012, players in this position have won more Super Bowl MVP awards (26 of 47) than players at all other positions combined.
|“||[T]he most glorified — and scrutinized — position in team sports.||”|
—Los Angeles Times, January 2012
The presence or absence of a star quarterback usually greatly affects the team. For example, by ensuring that the team would be able to select Robert Griffin III of Baylor University in the 2012 draft, the Washington Redskins likely became more attractive for free agents who wished to play with the Heisman Trophy winner. By contrast, the Indianapolis Colts—among the most successful franchises in any sport during the 2000s with quarterback Peyton Manning—had a 2-14 record in 2011 because of injuries that prevented Manning from playing. A non-star quarterback on a winning team may be called a "game manager" if he avoids making mistakes that prevent his team's defense and rushing offenses from succeeding.
As the term "quarterback" gained acceptance in the 1930s, it originally referred to the player's position relative to other members of the offensive backfield. Before the emergence of the T-formation in the 1940s, all members of the offensive backfield were legitimate threats to run or pass the ball, and most teams used four offensive backs on every play: a quarterback, two halfbacks, and a fullback. The quarterback began each play a quarter of the way back, the halfbacks began each play side by side and halfway back, and the fullback began each play the farthest back. Now that most offensive formations have only one or two running backs, the original designations do not mean as much, as the fullback is now usually a lead blocker (technically a halfback), while the halfback or tailback (called such because he stands at the "tail" of the I) lines up behind the fullback.
Traditionally, quarterbacks have been responsible for calling the team's offensive plays based on the defense's formation, or game situation. To choose the proper play, quarterbacks often spend time rehearsing and studying prearranged plays during their team's practice sessions.
In recent years, the rise of offensive coordinators has led partiality toward a scripted game plan. The offensive coordinators and coaches usually give the quarterback information via a built-in headphone in the helmet as to what to do before the play. Quarterbacks are allowed to hear, but not talk to, their coaches until there are fifteen seconds left on the play clock. The quarterback then relays the information to teammates and executes the plays. When the players are set in a formation, the quarterback starts the play by calling out a code word, a number, or a combination of the two.
Dallas Cowboys head coach Tom Landry was an early advocate of taking play calling out of the quarterback's hands. Although this remained a common practice in the NFL through the 1970s, fewer QBs were doing it by the 1980s and even Hall-of-Famers like Joe Montana did not call their own plays. Buffalo Bills QB Jim Kelly was one of the last to regularly call plays. Among current NFL QBs, Peyton Manning of the Denver Broncos has been known to call all, or nearly all, of his team's plays using a no-huddle offense—although late in his tenure with the Indianapolis Colts, his center Jeff Saturday had equal say in making adjustments and calling audibles. Similarly, Baltimore Ravens quarterback Joe Flacco retains a high degree of control over the offense, particularly when running a no-huddle scheme.
Special tactics 
If quarterbacks are uncomfortable with the formation the defense is using, they may call an audible change to their play. For example, if a quarterback receives the call to execute a running play, but he notices that the defense is ready to blitz—that is, to send additional defensive backs across the line of scrimmage in an attempt to tackle the quarterback or thwart his ability to pass—the quarterback may want to change the play. To do this, the quarterback yells a special code, like "Blue 42," or "Texas 29," which tells the offense to switch to a specific play or formation.
Also, quarterbacks can "spike" or throw the football at the ground to stop the official game clock. For example, if a team is down by a field goal with only seconds remaining, a quarterback may spike the ball to prevent the game clock from running out. This usually allows the field goal unit to come onto the field, or attempt a final "Hail Mary pass". However, if a team is winning, a quarterback can keep the clock running by kneeling after the snap. This is normally done when the opposing team has no timeouts and there is little time left in the game, as it allows a team to burn up the remaining time on the clock without risking a turnover or injury.
While quarterbacks are mainly not a factor in terms of receiving forward passes, some trick plays, like the flea flicker, require quarterbacks to catch a lateral by a wide receiver or running back before delivering a forward pass. In the wildcat formation, a quarterback lines up as a flank receiver who can be used to catch a forward pass. Typically the quarterback is not thrown to in this formation, but serves as a decoy, as even the least mobile quarterbacks are capable of catching a ball for positive yardage. Occasionally, some backup quarterbacks may be used to receive long snaps as a holder for field goal or extra point attempts, as quarterbacks generally have good ball handling skills, and may have to become the passer in the event of a bad snap, an aborted kick attempt or a designed trick play.
Under NFL rules, if a quarterback lines up under center, he is by definition ineligible and not allowed to receive a forward pass. However, in college and high school ball, quarterbacks are eligible receivers (by a special exemption in the high school rule books) regardless of whether they are under center or in a shotgun formation. The NFL allows a quarterback in a shotgun formation to receive a forward pass.
Dual-threat quarterbacks 
A dual-threat quarterback possesses the skills and physique to run with the ball if necessary. With the rise of several blitz heavy defensive schemes and increasingly faster defensive players, the importance of a mobile quarterback has been redefined. While arm power, accuracy, and pocket presence – the ability to successfully operate from within the "pocket" formed by his blockers – are still the most important quarterback virtues, the ability to elude or run past defenders creates an additional threat that allows greater flexibility in the team's passing and running game.
Dual-threat quarterbacks have historically been more prolific at the college level. Typically, a quarterback with exceptional quickness is used in an option offense, which allows the quarterback to either hand the ball off, run it himself, or pitch it to the running back following him at a distance of three yards outside and one yard behind. This type of offense forces defenders to commit to either the running back up the middle, the quarterback around the end, or the running back trailing the quarterback. It is then that the quarterback has the "option" to identify which match up is most favorable to the offense as the play unfolds and exploit that defensive weakness. In the college game, many schools employ several plays that are designed for the quarterback to run with the ball. This is much less common in professional football, except for a quarterback sneak, but there is still an emphasis on being mobile enough to escape a heavy pass rush.
Super Bowl XXIX MVP and Hall of Famer Steve Young was famously known for being a dual-threat quarterback. He was the first player ever to win the Super Bowl with the most touchdowns (6) and being the leading rusher of the game. NFL quarterbacks who have rushed for more than 30 yards per game in a season (minimum 10 games) are Michael Vick (7 seasons), Randall Cunningham (6 seasons), Steve Young (4 seasons), Donovan McNabb (3 seasons), Steve McNair (3 seasons), Tobin Rote (3 seasons), Daunte Culpepper (3 seasons), Bobby Douglass (3 seasons), Cam Newton (2 seasons), Vince Young (1 season), Rich Gannon (1 season), Kordell Stewart (1 season), Johnny Lujack (1 season), Bobby Layne (1 season), Mark Brunell (1 season), Ryan Tannehill (1 season), Russell Wilson (1 season), Tim Tebow (1 season), Colin Kaepernick (1 season), Robert Griffin III (1 season) and Steve Grogan (1 season). Michael Vick owns NFL quarterback records for single-season rushing yards (1,039 in 2006) and career rushing yards (5,551).
Here are the Top 10 NFL single-season rushing performances for a quarterback:
1) Michael Vick, 1,039 yards, 2006 Atlanta Falcons
2) Bobby Douglass, 968 yards, 1972 Chicago Bears
3) Randall Cunningham, 942 yards, 1990 Philadelphia Eagles
4) Michael Vick, 902 yards, 2004 Atlanta Falcons
5) Robert Griffin III, 815 yards, 2012 Washington Redskins
6) Michael Vick, 777 yards, 2002 Atlanta Falcons
7) Cam Newton, 741 yards, 2012 Carolina Panthers
8) Cam Newton, 706 yards, 2011 Carolina Panthers
9) Michael Vick, 676 yards, 2010 Philadelphia Eagles
10) Steve McNair, 674 yards, 1997 Tennessee Oilers
Two quarterback system 
Some teams employ a strategy which involves the use of more than one quarterback during the course of a game. This is more common at lower levels of football, such as high school or small college, but rare in major college or professional football.
There are three circumstances in which a two-quarterback system may be used.
The first is a circumstance in which a team is in the process of determining which quarterback will eventually be the starter, and may choose to use each quarterback for part of the game in order to compare the performances.
The second, still occasionally seen in major-college football, is the use of different quarterbacks in different game or down/distance situations. Generally this involves a running quarterback and a passing quarterback in an option or wishbone offense. This strategy had all but disappeared from professional football, but returned to some extent with the advent of the "wildcat" offense. There is a great debate within football circles as to the effectiveness of the so-called "two quarterback system" Many coaches and media personnel remain skeptical of the model.
The third is a starter/reliever system, in which the starting quarterback may be replaced later in the game if ineffective. This is distinct from a situation in which a starter is benched in favor of the back-up because the switch is part of the game plan, and the expectation is that the two players will assume the same roles game-after-game. This strategy is rare, and was last seen in the NFL in the "WoodStrock" combination of Don Strock and David Woodley, which took the Miami Dolphins to the Epic in Miami and Super Bowl XVII the following year.
See also 
- American football quarterbacks
- Canadian Football League quarterbacks
- List of quarterbacks with multiple Super Bowl wins
- David S. Neft, Richard M. Cohen, and Rick Korch, The Football Encyclopedia: The Complete History of Professional Football, From 1892 to the Present (St. Martin's Press 1994), ISBN 0-312-11435-4
- Farmer, Sam (2012-01-28). "In the NFL, it's (almost) all about the quarterback". Los Angeles Times. Retrieved January 28, 2012.
- White, Joseph (2012-03-12). "RGIII should help Redskins attract free agents". Sports Illustrated. Associated Press. Retrieved March 30, 2012.
- Mayer, Larry, When does radio communication get cut off? (August 15, 2007), chicagobears.com. Retrieved on August 16, 2007.
- Layden, Tim (September 24, 2012). "Calm Amid The Chaos". Sports Illustrated. Retrieved December 12, 2012.
- In two-QB formats, there's no time to waste in securing the anchors for your fantasy squad - Fantasy Football - ESPN
|Positions in American football and Canadian football|
|Linemen||Guard, Tackle, Center||Linemen||Tackle, End, Nose tackle||Kicking players||Placekicker, Punter, Kickoff specialist|
|Quarterback||Linebackers||Snapping||Long snapper, Holder|
|Backs||Halfback (Tailback), Fullback, H-back||Backs||Cornerback, Safety, Halfback||Returning||Punt returner, Kick returner|
|Receivers||Wide receiver, Tight end, Slotback||Nickelback, Dimeback||Tackling||Gunner|
|Formations (List) — Nomenclature|