American football strategy

American football strategy is the strategic deployment of players and assignment of tasks to offensive and defensive players of American football. It derives by analogy from military strategy as the science and art of command as applied to the overall planning and conduct of play
In early American football, the planned strategy of offensive players ("plays") and positioning and assignment of defensive players ("coverage") was rudimentary. As the game evolved, plays and coverage become more complex, and roles for offensive and defensive players became more exact and demanding. Modern strategy involves certain conventions and assignments, but can also use legal but unorthodox patters, often called trick plays, to surprise an opponent.
The rules of professional and college American football permit a broad range of assignments and deployment of offensive and defensive players. Much of the excitement in American football derives from the lightning-quick unfolding of offensive and defensive strategies matched against each other, and the tactical ability of individual players to adapt and react to counter the opponent's strategy.
Football strategy takes many forms, and is not always about the strength and size of the two teams. Teams must execute strategy in three phases of the game: offense, defense, and special teams.


Offensive strategy
The goal of offensive strategy is to move the ball to score more points than the opponent and to prevent the opponent from doing the same by reducing the amount of game clock time remaining, denying the opponent possession of the ball, and preventing them from advancing the ball into scoring position. In order to do so, coaches and players choose to execute selected plays based on a variety of factors including the opponent’s defensive strategy; the talent, skill, health, and experience of the players on both the offensive and defensive teams; the amount of time remaining before halftime or the end of the game; and the number of points that either team would need to score in order to take the lead and win the game.

Offensive players
On offense, there are four types of players: linemen, backs, quarterbacks, and receivers. The above-mentioned considerations will determine what formations and plays the team will run. The basic offensive positions and those players' duties vary from one offensive scheme to another.
The position name (as well as the initial abbreviations recognized by coaches, players, and fans alike, shown in quotes below) may vary from one team's playbook to another, but these are the ones most commonly used:

Linemen
Center: The Center ("C") is the player who snaps the ball to the quarterback. Like the other four linemen, his job consists of both run blocking, which means pushing the defenders away from the ball carrier on a running play, and pass blocking, which means stopping the defenders from disrupting or tackling the passer. The center is also usually responsible for calling the blocking schemes on the line, directing the other linemen on who blocks whom.
Guard: Guards ("G") line up on both sides of the center. The guards are generally bigger than the center and are typically better run blockers than pass blockers.
Tackle: Tackles ("T") are the "bookends" of the offensive line. They are usually the biggest offensive linemen (at the NFL level they are typically at least 300 lbs (136 kg), and as tall as 6'9" (205 cm)), but also must be agile enough to thwart any outside pass rush. If a team has a righthanded quarterback, the left tackle is usually the best pass blocker on the line to prevent a "blindside" pass rush the quarterback might not see. Generally, tackles ideally have great "hands" and even better foot work. Left tackles are the most highly valued players on an offensive line as most quarterbacks are righthanded.

Backs
Quarterback: The Quarterback ("QB") lines up directly behind center. The quarterback must take the ball from the Center (in a motion called the 'snap') and put it into play. In most offenses, his primary duty is either passing (throwing) the ball or making the opposing team believe he is going to pass the ball while actually handing it off to a running back ("RB") who carries the ball downfield. Since passing the ball is an offense's quickest way to advance the ball, a team must have a quarterback who can throw the ball accurately and make quick, correct decisions as to which player is in the best position to receive the throw. In some offenses, the quarterback is often called upon to run the ball downfield as part of the play, and a quarterback might have to take the ball and run if his screen of protective players breaks down and there are no open receivers. On "trick plays" sometimes the quarterback becomes the receiver, depending on the alignment, wherein a running back or wide receiver attempts a pass to him, after a hand-off, direct snap from the center, or lateral pass from the quarterback to either position. The Quarterback is considered by many to be the most important player on the field. The QB is the leader of the offense. He communicates to the players the play they are going to run, in the huddle before the team lines up to execute the play. There are many different types of QB's. Some are very fast and agile and can be considered a double threat because they are able to both throw and run the ball. Some are not very mobile and require great protection from their lineman in order to execute the play. Important QB attributes starting with most to least important are as follows: vision and ability to read defenses and find receivers, throwing accuracy, throwing power, and mobility.
Wingback: is traditionally only used in the Wing T formation. He may also line up just outside and behind the tight end and be used to either block on the outside or run a pass route or a sweep.
Fullback: The Fullback ("FB") is also a running back, but in recent years, the fullback position has developed into more of a blocking back, and in some schemes a receiver. The fullback is usually the bigger, more physical of the two running backs, and so the quarterback will often hand the ball to his fullback in short yardage situations where the defense may assume that the offense will use a running play, as opposed to a passing play, and therefore bring more defenders to the line of scrimmage to defend against a run.
Running back: If a team is to have an effective running game, it falls on this player's shoulders. He may have blocking duties in some offenses and on some plays he may become a receiver, but in most offenses, the running back is there to run the ball. Historically, this position was known as "halfback" ("HB") or "tailback" ("TB"), depending on the offensive scheme; these terms are still used to a lesser extent. Like Quarterbacks, there are many different types of running backs. Some are very large and therefore difficult to bring down, some are smaller and very fast. Important runningback attributes are as follows: vision which attributes to the ability to find holes, follow and read blocks, and react to defensive of players, speed, power, agility, receiving ability, and blocking ability. The "running back" designation is often applied to fullbacks as well. The RB is considered a do it all player, he may even throw the ball on trick plays.

Receivers
Wide receiver: Depending on the formation, an offense may have anywhere from zero to five wide receivers ("WR"). Most base formations feature two WRs, though three-WR formations are common as well. A WR who lines up on the line of scrimmage may be referred to as a Split End, while a WR off the line of scrimmage may be called a Flanker, Wingback or Slotback. WRs are among the fastest and most agile players on the team and their job is to get "open" (create separation between themselves and defenders), catch the ball when thrown to them, and run after the catch. Well-rounded receivers are also effective downfield blockers, though effectiveness in that regard is secondary to their pass-catching role.
Tight end: The Tight End ("TE") was traditionally a blocking position but is now considered a hybrid wide receiver/lineman. TEs are among the most well-rounded athletes on the field as they must be strong enough to run block and pass block, and agile enough to run pass routes and effectively catch the football. A TE's size presents matchup problems for smaller defenders, such as cornerbacks, while their speed gives them an advantage versus larger but slower defenders such as linebackers. In the 1980s, Washington Redskins coach Joe Gibbs developed a hybrid TE/fullback position called "H-Back"; this player is usually TE-sized and replaces the fullback on the field, but has more pass-catching responsibility and less running unless "flexed" to the usual FB alignment. The H-Back may line up as a second TE on the opposite side from the first, but most commonly lines up immediately behind the first TE. Consequently, that position is still important in the Redskins' offense as of 2007.

Offensive formations
Before the ball is snapped the offensive team lines up in a formation. Most teams have a "base" formation they prefer to line up in, while other teams leave the defense guessing. Teams will often have "special formations" which they only use in obvious passing situations, short yardage or goal line situations, or formations they have developed for that particular game just to confuse the defense. Because there are a nearly unlimited number of possible formations, only a few of the more common ones are listed below.