A fullback (FB) is a position in the offensive backfield in gridiron football, and is one of the two running back positions along with the halfback. Fullbacks are typically larger than halfbacks and in most offensive schemes the fullback's duties are split among power running, pass catching, and blocking for both the quarterback and the other running back. 
Many great runners in the history of American football have been fullbacks, including Jim Brown, Marion Motley, Bronko Nagurski, Jim Taylor, Franco Harris, Larry Csonka, John Riggins, Christian Okoye, and Levi Jackson. However, many of these runners would retroactively be labeled as halfbacks, due to their position as the primary ball carrier; they were primarily listed as fullbacks due to their size and did not often perform the run-blocking duties expected of modern fullbacks. Examples of players who have excelled at the hybrid running–blocking–pass-catching role include Vonta Leach, Mike Alstott, William Henderson, Daryl Johnston, Kyle Juszczyk, John Kuhn, Le'Ron McClain, Lorenzo Neal, Marcel Reece, and Tom Rathman.
In the days before two platoons, the fullback was usually the team's punter and drop kicker.  When, at the beginning of the 20th century, a penalty was introduced for hitting the opposing kicker after a kick, the foul was at first called "running into the fullback", inasmuch as the deepest back usually did the kicking. 
Before the emergence of the T-formation in the 1940s, most teams used four offensive backs, lined up behind the offensive line, on every play: a quarterback, two halfbacks, and a fullback. The quarterback began each play a quarter of the way "back" behind the offensive line, the halfbacks began each play side by side and halfway "back" behind the offensive line, and the fullback began each play the farthest "back" behind the offensive line.
As the game evolved and alternate formations came in and went out of fashion, halfbacks (reduced to typically just one rather than two) emerged as the offensive backs most likely to run the ball. "Halfback" came to be synonymous with "running back". Formations began to favor placing the fullback—the back most entrusted with blocking for the running back—closer to the line of scrimmage than the running back. These blocking backs retained the name "fullback" even though they were closer to the offensive line than the halfback. The term "halfback" declined in usage, replaced variously with the more descriptive term "tailback" or the generic term "running back".
In the modern game, when the quarterback is under center, the fullback most often lines up directly behind the quarterback and in front of the halfback or tailback. The fullback position has seen a decline in recent time, with only 17 full-time fullbacks playing in 2016. The trend can be traced back to teams choosing to pass more, the use of "11 personnel" (one running back and one tight end), and the use of hybrid "H-backs". 
Fullbacks are typically known less for speed and agility and more for muscularity and the ability to shed tackles. In 2010s NFL, fullbacks, while occasionally deployed as ball carriers, are often primarily a lead blocker to allow running backs to get to the secondary of the opposing team's defense. In the early 2000s, many NFL teams used blocking fullbacks, such as Tony Richardson, Vonta Leach, and Lorenzo Neal, with great success. These backs cleared the way for some of the decade's great running backs. Later on, some teams have phased the fullback position out of their offense altogether, with those teams either all but eschewing the I-formation, or instead utilizing either a tight end, h-back, or backup running-back in the role.
Prominent fullbacks in the NFL as of 2022 include C. J. Ham, Andy Janovich, Jamize Olawale, Reggie Gilliam, Patrick Ricard, Alec Ingold, Bruce Miller, Cullen Gillaspia, Anthony Sherman, Kyle Juszczyk, and Keith Smith. In spite of their usually infrequent carries, some fullbacks have led their teams in rushing – among the most notable ones were Le'Ron McClain who was the rushing leader for the Baltimore Ravens in 2008 and Tony Richardson who led the Kansas City Chiefs in rushing in 2000. In 2010, Peyton Hillis led the Cleveland Browns in rushing yards with 1,177 yards as a fullback before being converted into a halfback.
Although technically running backs, typically fullbacks are primarily valued for their blocking in most 21st century offenses. The most common and simple runs—the dive and the blast—both employ the fullback as the primary blocker for the halfback. In the flexbone formation, however, the fullback (sometimes referred to as the B-back) can often be used as the primary rushing threat.
In many other offensive schemes, the fullback is used as a receiver, especially when the defense blitzes. In selected plays, some teams will have a lineman report as an eligible receiver to line up as a fullback ("Jumbo" or "Heavy Jumbo") or as a tight end in a "Miami" package in goal-line formations. Players who have been frequently used as situational fullbacks include Haloti Ngata, Dontari Poe, Jared Allen while with the Kansas City Chiefs, Richard Seymour while with the New England Patriots, and Isaac Sopoaga while with the San Francisco 49ers, while Dan Klecko and Nikita Whitlock have played both as a defensive tackle and fullback. Defensive Tackle William "The Refrigerator" Perry scored a touchdown in Super Bowl XX from the fullback position.
Most teams in the NFL do not have a substitute fullback, though there are exceptions. The role can be filled by backup or number three or four tight ends or bigger and less-frequently-used running backs. Occasionally, defensive tackles have been used in the fullback position (famous examples include William "The Refrigerator" Perry and Kyle Williams); this is most commonly used in goal-line situations, where the defensive tackle's size and ability to penetrate a wall of players becomes an advantage. In modern offenses, fullbacks in an I-formation can be motioned into a 2-TE formation or H-back formation, making a running back or tight end fairly well suited to the role.
The fullback position is less frequently used in Canadian football, which focuses more on passing than running the ball.
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.
The tight end (TE) is an offensive position in American football, arena football, and Canadian football. It is a hybrid that combines the characteristics and roles of both an offensive lineman and a 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 and potent weapons in team's offensive schemes.
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.
American football positions have slowly evolved over the history of the sport. From its origins in early rugby football to the modern game, the names and roles of various positions have changed greatly, some positions no longer exist, and others have been created to fill new roles.
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.
In sports, a starting lineup is an official list of the set of players who will participate in the event when the game begins. The players in the starting lineup are commonly referred to as starters, whereas the others are substitutes or bench players.
Center or Centre (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.
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.
In American football, a T formation is a formation used by the offensive team in which three running backs line up in a row about five yards behind the quarterback, forming the shape of a "T".
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 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.
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, a back is a player who plays off of the line of scrimmage. Historically, the term "back" was used to describe multiple positions on offense and defense, although more descriptive and specific position naming is now common. Thus, "back" can refer to positions including:
A play calling system in American football is the specific language and methods used to call offensive plays.