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The passing pocket, or the pocket, is a term used in American football to describe the area in the backfield created on a passing play where the offensive line forms a wall of protection around the quarterback.  This allows him adequate time to find an open receiver and to pass the ball. The offensive line will drop back slightly, creating a U-shaped protected area for the quarterback to find an open receiver and pass the ball. 
If the quarterback is unable to find an open receiver, he will attempt to run the ball himself, throw the ball out of bounds to prevent a sack and/or turnover, or if there is no lane, may collapse to the ground to protect the ball and try to avoid a fumble. Even with a well structured offensive line, the quarterback only has seconds to pass the ball within the pocket. Moving the pocket can help avoid a sack.  When that fails, quarterbacks may scramble (run around behind the line of scrimmage), either to gain more time for the wide receivers, to avoid a sack, or to rush the ball.
The area between the two tackles on the offensive line is referred to as the tackle box. This area itself can be formed using different types of protections to keep the quarterback safe.  The offensive tackles set the depth of the tackle box by kick sliding back to around six yards after the snap of the ball. The guards are next in depth and will drop back to around three to four yards and will defend the middle of the pocket along with the center. The different drop-back depths of the linemen helps to create enough space for the quarterback to go through his throwing motion. Sometimes tight ends and running backs may be used as extra blockers to solidify the pocket.
There are many different player personnel packages that can be used to protect the quarterback. The pocket could be protected by five linemen, two tight ends, as well as two running backs. When two running backs are used, they do constitute the tackle box but they are typically used to clear any stray rushers that may get past the inner linemen. They are used to create more space for the quarterback to step into in order to make a good throw. There can be one or two running backs used along with one or two tight ends depending on the packages called for. Sometimes, running backs and tight ends will partially block an advancing defender quickly, or what's known as "chip blocking" an advancing defender, and then they will go run their receiving route.
Tight ends can do the same thing, which means that the tackles would then have to set the depth of the tackle box.
The defense is trying to break down the tackle box as quickly as possible. They will try to send extra rushers to outnumber the blockers. Another tactic would be to send speed rushers off either side of the offensive line to run around the tackles before they can set the depth of the tackle box. The defensive ends are sometimes able to run past the tackles and get to the quarterback before he can step up into the tackle box to protect himself better. Another maneuver that is used is the middle blitz where the defense sends multiple rushers up the middle of the line in order to get past the center and guards to collapse the tackle box and sack the quarterback. The offensive line cannot block up the middle when too many rushers are running at them. This rushes the quarterback and forces him to get rid of the ball before he is ready to do so. There are many different types of blitzes but their only purpose is to confuse the blockers and ruin the tackle box that is being formed.
When the defense succeeds in their goal of confusing the offensive linemen, major problems form for the quarterback. The term that is used when the defense is getting close to the quarterback is that the tackle box is collapsing. When the tackle box collapses, the quarterback is trained to do one of a few different things: to scramble out of the tackle box and look to gain yards by running, to get outside of the tackle box and throw the ball out of bounds, or—in extreme situations—to just take the sack and not lose possession of the football. While the pocket will always collapse eventually, situations where the pocket collapses faster than anticipated create a difficult conundrum for quarterbacks, as they are faced with a plethora of possible choices with virtually no time to choose between them. A quarterback who is able to effectively react to the pocket collapsing and salvage the play is said to have good pocket awareness or pocket presence. 
A running back (RB) is a member of the offensive backfield in gridiron football. The primary roles of a running back are to receive handoffs from the quarterback to rush the ball, to line up as a receiver to catch the ball, and block. There are usually one or two running backs on the field for a given play, depending on the offensive formation. A running back may be a halfback, a wingback or a fullback. A running back will sometimes be called a "feature back" if he is the team's starting running back.
In gridiron football, a lineman is a player who specializes in play at the line of scrimmage. The linemen of the team currently in possession of the ball are the offensive line, while linemen on the opposing team are the defensive line. A number of NFL rules specifically address restrictions and requirements for the offensive line, whose job is to help protect the quarterback from getting sacked for a loss, or worse, fumbling. The defensive line is covered by the same rules that apply to all defensive players. Linemen are usually the largest players on the field in both height and weight, since their positions usually require less running and more strength than skill positions.
Linebacker (LB) is a playing position in gridiron football. Linebackers are members of the defensive team, and line up three to five yards behind the line of scrimmage and the defensive linemen. They are the "middle ground" of defenders, playing closer to the line of scrimmage than the defensive backs (secondary), but farther back than the defensive linemen.
In gridiron football, a sack occurs when the quarterback is tackled behind the line of scrimmage before throwing a forward pass, when the quarterback is tackled behind the line of scrimmage in the "pocket" and without clear intent, or when a passer runs out of bounds behind the line of scrimmage due to defensive pressure. This often occurs if the opposing team's defensive line, linebackers or defensive backs are able to apply pass pressure to quickly get past blocking players of the offensive team, or if the quarterback is unable to find a back to hand the ball off to or an available eligible receiver to catch the ball, allowing the defense a longer opportunity to tackle the quarterback.
A screen pass is a play in gridiron football consisting of a short pass to a receiver who is protected by a screen of blockers. During a screen pass, a number of things happen concurrently in order to fool the defense into thinking a long pass is being thrown, when in fact the pass is merely a short one, just beyond the defensive linemen. Screens are usually deployed against aggressive defenses that rush the passer. Because screens invite the defense to rush the quarterback, they are designed to leave fewer defensemen behind the rushers to stop the play.
In gridiron football, blitzing is a tactic used by the defense to disrupt pass attempts by the offense. During a blitz, a higher than usual number of defensive players will rush the opposing quarterback, in an attempt either to tackle them or force them to hurry his pass attempt.
Strategy forms a major part of American football. Both teams plan many aspects of their plays (offense) and response to plays (defense), such as what formations they take, who they put on the field, and the roles and instructions each player are given. Throughout a game, each team adapts to the other's apparent strengths and weaknesses, trying various approaches to outmaneuver or overpower their opponent in order to win the game.
In American football, a bootleg play is a play in which the quarterback runs with the ball in the direction of either sideline behind the line of scrimmage. This can be accompanied by a play action, or fake hand off of the ball to a running back running the opposite direction.
The 46 defense is an American football defensive formation, an eight men in the box defense, with six players along the line of scrimmage. There are two players at linebacker depth playing linebacker technique, and then three defensive backs. The 46 defense was originally developed and popularized with the Chicago Bears by their defensive coordinator Buddy Ryan, who later became head coach of the Philadelphia Eagles and Arizona Cardinals.
A formation in American football refers to the position players line up in before the start of a down. There are both offensive and defensive formations and there are many formations in both categories. Sometimes, formations are referred to as packages.
Single set back is an offensive base formation in American football which requires only one running back lined up about five yards behind the quarterback. There are many variations on single back formations including two tight ends and two wide receivers, one tight end/three wide receivers, etc. The running back can line up directly behind the quarterback or offset either the weak side or the strong side.
A trick play, also known as a gadget play, gimmick play or trickeration, is a play in gridiron football that uses deception and unorthodox tactics to fool the opposing team. A trick play is often risky, offering the potential for a large gain or a touchdown if it is successful, but with the chance of a significant loss of yards or a turnover if not. Trick plays are rarely used not only because of the riskiness, but also to maintain the element of surprise for when they are used.
A halfback (HB) is an offensive position in American football, whose duties involve lining up in the offensive backfield and carrying the ball on most rushing plays, i.e. a running back. When the principal ball carrier lines up deep in the backfield, and especially when that player is placed behind another player, as in the I formation, that player is instead referred to as a tailback.
In American football, the specific role that a player takes on the field is referred to as their "position". Under the modern rules of American football, both teams are allowed 11 players on the field at one time and have "unlimited free substitutions", meaning that they may change any number of players during any "dead ball" situation. This has resulted in the development of three task-specific "platoons" of players within any single team: the offense, the defense, and the so-called 'special teams'. Within these three separate "platoons", various positions exist depending on the jobs that the players are doing.
The flexbone formation is an offensive formation in American football that includes a quarterback, five offensive linemen, three running backs, and varying numbers of tight ends and wide receivers. The flexbone formation is a predominant turnover formation derived from the wishbone formation and it features a quarterback under center with a fullback lined up directly behind the quarterback. There are two smaller running backs called slotbacks aligned behind the line of scrimmage on each side of the offensive line. The slotbacks are sometimes incorrectly referred to as wingbacks. But in order to be a wingback, there must be a guard, tackle and tight end all on one side of the center on the line of scrimmage and then the wingback off the line of scrimmage.
The triple option is an American football play used to offer several ways to move the football forward on the field of play. The triple option is based on the option run, but uses three players who might run with the ball instead of the two used in a standard option run.
In American football, a play is a close-to-the-ground plan of action or strategy used to move the ball down the field. A play begins at either the snap from the center or at kickoff. Most commonly, plays occur at the snap during a down. These plays range from basic to very intricate. Football players keep a record of these plays in a playbook.
In American football, the 3–4 defense is a common defensive alignment consisting of three down linemen and four linebackers. It is a called a "base defense" because it will readily switch to other defensive alignments as circumstances change. Alternatively, some defenses use a 4–3 defense.
The following terms are used in American football, both conventional and indoor. Some of these terms are also in use in Canadian football; for a list of terms unique to that code, see Glossary of Canadian football.