Science Fair Project Encyclopedia
The quarterback is a position in the offensive backfield of American and Canadian football, directly behind players of the "line". He is generally the leader of the offensive team when it is on the field, responsible for initiating play by receiving the snap of the ball from the center .
After snapping the ball, the quarterback typically attempts to pass the ball or hand it to another player, or attempt to advance it himself. If the quarterback is tackled behind the line of scrimmage, it is known as a sack.
That description covers the so-called "T" quarterback, meaning the quarterback in the T and formations derived from it. This is far and away the most common usage; however, not all formations have a quarterback, and that in those that do, the quarterback is not necessarily positioned to take snaps.
The term quarterback has its origin in Scottish rugby, wherein backfield players, according to their customary distance behind the forwards, were designated "quarter back" (i.e. 1/4 of the way back), "half back", and "full back". Eventually in rugby the English-Irish nomenclature prevailed, with halfback, three-quarters back, and fullback; in some places the term "five-eighths back" is used as well.
Throughout much of the history of the professional game, the quarterback called the team's offensive plays while on the field, based on the flow of the game and a reading of the defense. The "plays" are pre-arranged and practiced plans the team will use to try to move the ball downfield. The play itself is given to the other offensive players in the huddle before the offensive team lines up for the "snap," which is the start of the offensive team's attempt to move the ball past the defense.
In recent years, with the rising importance of offensive coordinators and their reliance on scripted game plans and the use of radio headsets, the quarterback now usually receives which play to call from the coach on the sidelines. In 2003, the only quarterback in the NFL who routinely called his own plays was Peyton Manning of the Indianapolis Colts.
The quarterback also often gets to choose the "count" of the cadence for the snap. The quarterback usually calls out the signal for the ball to be snapped and may optionally change the play at the line of scrimmage before the ball is snapped by shouting out additional signals to the other players on his team. This is known as calling an audible. A typical cadence might be something like, "Down, Set, Hut", where the ball is snapped on "Hut". If an audible were to be called, it would be shouted somewhere between "Down" and "Hut". For strategy, the ball may be snapped on "Set" or after multiple shouts of "Hut" to catch the defensive team off guard. This is what is meant by the count of the cadence, or the "snap count".
In the modern game, quarterbacks are typically evaluated on their passing statistics, including total yardage, completion ratio, touchdowns, and the ability to avoid interceptions. Up through the 1990s, most of the prominent NFL quarterbacks were "drop back passers", who typically took between five and seven steps behind the line of scrimmage immediately after snapping the ball to look for an open passing receiver down field.
In a more intangible sense, however, quarterbacks are evaluated on their ability to lead a team to victory, especially in close games. A quarterback who possesses the ability to dictate the flow of the game as a whole and to score points in critical situations is ultimately considered more valuable than one with good statistics who cannot lead his team to victory over time.
In recent years in the NFL, partially in response to more mobile defensive linemen and increased use of the "blitz" defense, there has been a resurgence in the importance of the "running quarterback", whose mobility, speed,and power allows him the opportunity to gain yardage by running around the outside of the defensive line, even after initially dropping back to pass. Although the emphasis of quarterback's performance is still on his passing abilities, such running ability provides an additional threat that allows greater flexibility in the team's passing game.
(See Category:American football quarterbacks for notable individuals)
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