A defensive tackle (DT) is a position in American football that will typically line up on the line of scrimmage, opposite one of the offensive guards, however he may also line up opposite one of the tackles. Defensive tackles are typically the largest and strongest of the defensive players. Depending on a team's individual defensive scheme, a defensive tackle may be called upon to fill several different roles. These roles may include merely holding the point of attack by refusing to be moved, or penetrating a certain gap between offensive linemen to break up a play in the opponent's backfield. If a defensive tackle reads a pass play, his primary responsibility is to pursue the quarterback, or simply knock the pass down at the line if it is within arm's reach. Other responsibilities of the defensive tackle may be to pursue the screen pass or drop into coverage in a zone blitz scheme. In a traditional 4–3 defense, there is no nose tackle. Instead there is a left and right defensive tackle.  Some teams, especially in the National Football League (NFL), have a nose tackle in this scheme, but most of them do not.
Nose tackle (also nose guard or middle guard) is a defensive alignment position for a defensive lineman. In the 3–4 defensive scheme the sole defensive tackle is referred to as the nose tackle.  The nose tackle aligns across the line of scrimmage from the offense's center before the play begins in the "0-technique" position.  In this position, frequently taking on the center and at least one if not both of the guards, the nose tackle is considered to be the most physically demanding position in gridiron football.  In five-linemen situations, such as a goal-line formation, the nose guard is the innermost lineman, flanked on either side by a defensive tackle or defensive end. According to Pat Kirwan, a traditional 3–4 defense demands "a massive man who can clog up the middle," while a 4–3 defense is looking for "a nose tackle who relies on quickness to penetrate and move along the front." 
Typical 3–4 nose tackles are "big wide bodies who can hold the point of attack and force double teams by the guard and center."  They are usually the heaviest players on the roster, with weights ranging from 320 to 350 pounds (145 to 159 kg). Also, height is critical, as they are supposed to get "under" the offensive line, which means ideal 3–4 nose tackles are no taller than 6 ft 3 in (1.91 m).  Recent examples of such nose tackles include Gilbert Brown, Casey Hampton, Jamal Williams, Vince Wilfork, and Damon Harrison. Rather uncommon are taller nose tackles, such as Bobby Brown III who is 6 ft 4 in (1.93 m) and Ted Washington, Ma'ake Kemoeatu, who are 6 ft 5 in (1.96 m) tall and each have won Super Bowl rings.
In some 4–3 defenses, the nose tackle is one of two defensive tackles. Some teams, especially in the NFL, have a nose tackle in the 4–3 defense, which lines up against the opposing center and very likely the weak-side or pulling guard. In a 4–3 defense, nose tackles are rather quick and supposed to "shoot the 'A gap' and beat the center and very likely the weak-side or pulling guard into the backfield."  Height is not as important, and their weight is closer to 300 pounds (136 kg).
The terms "nose guard" or "middle guard" were more commonly used with the five-man defensive line of the older 5–2 defense. Effective against most plays of the day, but with a weakness to the inside short pass, the 5–2 was phased out of the pro game in the late 1950s.   In the 4–3 defense, the upright middle linebacker replaced the middle guard. The nose guard is also used in a 50 read defense. In this defense there is a nose guard, two defensive tackles, and two outside linebackers who can play on the line of scrimmage or off the line of scrimmage in a two-point stance. The nose guard lines up head up on the center about six to eighteen inches off the ball. In a reading 50 defense, the nose guard's key is to read the offensive center to the ball. In run away, the nose guard's job is to shed the blocker and pursue down the line of scrimmage, taking an angle of pursuit. The primary responsibility of the nose tackle in this scheme is to absorb multiple blockers so that other players in the defensive front can attack ball carriers and rush the quarterback.
A 3-technique tackle (also 3-tech) or undertackle is often featured in a formation with four defensive linemen (such as the traditional 4–3 or the 4–2–5 Nickel defense), but can sometimes fill in as the nose tackle in a 3–4 defense. Compared to the 0 or 1-tech who is more prototypical of the nose tackle, the 3-tech is often a smaller, more agile defensive lineman (but still larger than the defensive ends) who specializes in penetrating through the line with his quickness as his bigger counterpart occupies blockers, aiming to sack the quarterback or tackle the rusher (often the running back) for a loss of yards. The 3-tech often lines up against the "weak side" of the offensive line, and therefore faces fewer double-teams as a result.  Notable examples of prototypical 3-tech tackles in the NFL include Geno Atkins, Sharrif Floyd, Tyrone Crawford, Kyle Williams, Ndamukong Suh, Aaron Donald, and Ed Oliver. Donald and Oliver, in particular, have pushed the limits on how small the 3-tech can be, both weighing just 285 lbs.  Their smaller statures have drawn criticism, but Donald and Oliver often make up for this using their athleticism. Donald has made eight Pro Bowls and was thrice named the AP Defensive Player of the Year. 
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.
The tight end (TE) is a position in American football, arena football, and Canadian football, on the offense. The tight end is often a hybrid position with the characteristics and roles of both an offensive lineman and a wide receiver. Like offensive linemen, they are usually lined up on the offensive line and are large enough to be effective blockers. On the other hand, unlike offensive linemen, they are eligible receivers adept enough to warrant a defense's attention when running pass patterns.
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.
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 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.
Center (C) is a position in gridiron football. The center is the innermost lineman of the offensive line on a football team's offense. The center is also the player who passes the ball between his legs to the quarterback at the start of each play.
In American football, a zone blitz is a defensive tactic that sends additional players to rush the opposing team's quarterback, whilst also unexpectedly redirecting a supposed pass rushing player into pass coverage instead. This tactic also likely includes zone coverage.
The Tampa 2 is an American football defensive scheme popularized by the Tampa Bay Buccaneers National Football League (NFL) team in the mid-1990s–early 2000s. The Tampa 2 is typically employed out of a 4–3 defensive alignment, which consists of four linemen, three linebackers, two cornerbacks, and two safeties. The defense is similar to a Cover 2 defense, except the middle linebacker drops into a deep middle coverage for a Cover 3 when he reads a pass play.
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.
There are several defensive formations commonly used in eight-man football. Defensive formations are classified by the total number of linemen and linebackers in the formation. The three basic types of formations in eight-man football are seven-man fronts, six-man fronts and five-man fronts.
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 is the default defensive alignment used on "base downs". However, defenses will readily switch to other defensive alignments as circumstances change. Alternatively, some defenses use a 4–3 defense.
In American football, a 4–3 defense is a defensive alignment consisting of four down linemen and three linebackers. It is called a "base defense" because it is the default defensive alignment used on "base downs". However, defenses will readily switch to other defensive alignments as circumstances change. Alternatively, some defenses use a 3–4 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.
In American football, the 5–2 defense is a defensive alignment consisting of five down linemen and two linebackers.
The 7–2–2 defense or seven-box defense, used seven "down linemen", or players on the line of scrimmage at the time of the snap, two linebackers, and two safeties. Amos Alonzo Stagg invented the seven-box defense in 1890 at Springfield College. At that time, most teams were using a nine-man line on defense, and there were only three downs and no forward passes. The 7–2–2 was the base defense used by Knute Rockne at Notre Dame, as well as Mike Donahue at Auburn. Into the late 1930s, the 7–2–2 was still commonly employed inside the defender's thirty-yard line. It was considered "very strong against a running attack, but rather weak defensively against passes." The 7–2–2 was also employed when the opponent was expected to punt.
The Miami 4–3, also called the 4–lslide, is a scheme closely associated with the Jimmy Johnson-led Miami Hurricanes, and taken by Johnson to the Dallas Cowboys. Built around Jimmy Johnson's notion of "upfield pressure", it is a penetrating, swarming defense, with a "get there firstest with the mostest" mentality. The focus is to cause opponents to make mistakes, even if the defense might give up a big gain or two. Compared to older 4–3 defenses, such as Tom Landry's 4–3 inside, the defensive line assignments are simpler. Linemen don't read then react, they act then read. Linebackers fill the gaps the linemen leave behind, ignoring gaps away from the play. Coverages are simple, and the playbook small and easy to learn.