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A running back (RB) is an American and Canadian football position who typically lines up in the offensive backfield. The primary roles of a running back are to receive handoffs from the quarterback for a rushing play, to catch passes from out of the backfield, and to 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 (in certain contexts also referred to as a tailback) or a fullback.
The halfback (HB) or tailback (TB) position is recognized as one of the more glamorous positions on the field, as it is often integral in both the passing and running attack. He is responsible for carrying the ball on the majority of running plays, and may frequently be used as a receiver on short passing plays. In today's game, an effective halfback must have a superior blend of both quickness and agility as a runner, as well as sure hands and shrewd vision upfield as a receiver. More and more quarterbacks depend on halfbacks as a safety valve receiver when primary targets downfield are covered or when they are under pressure. Occasionally, they line up as additional wide receivers. When not serving either of these functions, the primary responsibility of a halfback is to aid the offensive linemen in blocking, either to protect the quarterback or another player carrying the football. As a trick play, running backs are occasionally used to pass the ball on a halfback option play or halfback pass.
No position in Canadian/American football can perform his duties successfully without the help of other players. Like the wide receiver, who generally cannot make big plays without the quarterback passing to him (with the exception of the end-around or a reverse), the running back nearly always needs good blocking from the offensive line to successfully gain yardage. Also, a running back will generally have more rushing attempts than a receiver will have receptions, which is mainly because a receiver must catch a pass to obtain a reception, while a running back usually takes a direct handoff or short pitch from the quarterback before registering a rushing attempt.
Note that the difference between halfback and tailback is simply the position of the player in the team's offensive formation. In historical formations, the halfback lined up approximately half-way between the line of scrimmage and the fullback (similarly, quarterbacks line up a quarter of the distance between the line of scrimmage and the fullback). Because the halfback is usually the team's main ball carrier (while the fullback is primarily a blocker), modern offensive formations have positioned the halfback behind the fullback (at the "tail end" of the formation), to take advantage of the fullback's blocking abilities. As a result, some systems or playbooks will call for a tailback as opposed to a halfback.
The term tailback is often used in Canadian football interchangeably with running back, while the use of the term halfback is often exclusively reserved for the defensive halfback, which refers to the defensive back halfway between the linebackers and the cornerbacks.
In most modern college and professional football schemes, fullbacks (FB) carry the ball infrequently, instead using their larger physiques as primary "lead blockers". On most running plays, the fullback leads the halfback, attempting to block potential tacklers before they reach the ball carrier. When fullbacks are called upon to carry the ball, the situation typically calls for gaining a short amount of yardage, as the fullback can use his bulkiness to avoid being tackled early. Fullbacks are sometimes receivers for passing plays, although most plays call for the fullback to block any defensive players that make it past the offensive line, a skill referred to as "blitz pickup". Fullbacks are technically running backs, but today the term "running back" is usually used in referring to the halfback or tailback. Although fullbacks currently are rarely used as ball carriers, in previous offensive schemes fullbacks would be the designated ball carriers.
In high school football, where the offenses are simpler and player sizes vary greatly, fullbacks are still frequently used as ball carriers. In lower levels of the game (namely high school and college offenses), a scheme known as the "Triple Option" uses the fullback as a primary ball carrier. The fullback plays a unique role by establishing an inside running threat on every play. Triple Option fullbacks require excellent ball carrying skills and employ a tenacious running style, but often lack the receiving skills of their counterparts in other schemes. College teams such as Navy and Air Force have employed the triple option scheme with success.
While in years past the fullback lined up on the field for almost every offensive play, teams often opt to replace the fullback with an additional wide receiver or a tight end in modern football. Fullbacks in the National Football League rarely get to carry or catch the ball since they are used almost exclusively as blockers. Their talent and value to a team is usually judged by the success of the team's halfback or by how many times the team's quarterback is sacked, similar to the way offensive linemen are judged. Fullbacks are also still used occasionally as rushers on plays when a short gain is needed for a first-down or touchdown, as they are large and powerful and therefore effective at breaking through the line for a short distance. Jim Brown, Marion Motley, Franco Harris, and Larry Csonka are considered among the best fullbacks in history, all noted for a tough, grinding running style. In modern times, Daryl "Moose" Johnston, Lorenzo Neal, Tony Richardson, Sam Gash and Mike Alstott are considered among the greats.
Characteristics of a running back 
Height and weight 
There is a great diversity in those who play at the running back position. At one extreme are smaller (5'4"-5'10"), shiftier players. These quick, agile, and elusive running backs are often called "Scat backs" because their low center of gravity and maneuverability allow them to dodge tacklers. Prototypical "Scat backs" would be Darren Sproles, Warrick Dunn, Danny Woodhead, Ray Rice, and Maurice Jones-Drew.
At the other extreme are "power backs": bigger, stronger players who can break through tackles using brute strength and raw power. They are usually (but not always) slower runners compared to other backs, and typically run straight ahead (or "North-and-South" in football terminology) rather than dodging to the outside edges of the playing field (i.e. running "East-and-West") like shorter, quicker, lighter backs will often do. Jim Brown, Bo Jackson, Earl Campbell, Eddie George and Jerome Bettis can be considered typical "power backs"; Brandon Jacobs, Steven Jackson and Peyton Hillis are more recent examples.
Receiving ability 
Over the years, NFL running backs have been used more and more as receivers out of the backfield, especially with the rise in popularity of the West Coast offense and its variants. On passing plays, a running back will often run a "safe route," such as a hook or a flat route, that gives a quarterback a target when all other receivers are covered or when the quarterback feels pressured. Two backs, fullback Larry Centers and halfback Marshall Faulk, rank among the NFL's top 20 pass catchers.
Some teams have a specialist "third down back", who is skilled at catching passes or better at pass blocking and "picking up the blitz," and thus is often put in the game on third down and long. He can also be used to fool the defense by making them think he is being put into the game for a pass play, when the play is actually a run.
Running backs are also required to help the offensive line in passing situations, and, in the case of the full back, running plays. Running backs will often block blitzing linebackers or safeties on passing plays when the offensive line is occupied with the defensive linemen. On running plays, the fullback will often attempt to tear a hole in the offensive line for the running back to run through. Effective blocking backs are usually key components for a running back's success. On passing plays, a running back will stay back to help block and pick up the blitz.
Goal line backs 
Many teams also have a running back designated as a "goal line back" or "short yardage specialist". This running back comes into the game in short yardage situations when the offense needs only a little bit of yardage to get a first down or a touchdown. They also come into the game when the offense nears the goal-line. Normally when an offense gets inside the 5 yard line they send in their goal-line formation which usually includes 8 blockers, a quarterback, a running back, and a fullback. The closer they are to the goal-line the more likely they are to use this formation. If a certain running back is used often near the goal-line he is called the goal-line back. Short yardage and goal-line backs often are Power Backs that are not prone to fumbling. Their job is to get the first down or touchdown by muscling through or pushing a large mass of defenders to push their way to the designated area. A great example is Jerome Bettis who is widely considered the greatest running back in history at converting on 4th and 1.
Kick and punt returners 
Running backs are sometimes called upon to return punts and kickoffs, a role usually filled by wide receivers and defensive backs, such as cornerbacks, who are generally the fastest players on the team. A running back, Brian Mitchell, currently holds the NFL records for career kickoff return yards (14,014 yards) and career punt return yards (4,999). (Mitchell also gained 1,967 rushing yards, 2,336 receiving yards, and 14 fumble return yards, giving him a total of 23,330 all-purpose yards, the second-most in NFL history behind Jerry Rice.)
|Positions in American football and Canadian football|
|Linemen||Guard, Tackle, Center||Linemen||Tackle, End, Nose tackle||Kicking players||Placekicker, Punter, Kickoff specialist|
|Quarterback||Linebackers||Snapping||Long snapper, Holder|
|Backs||Halfback (Tailback), Fullback, H-back||Backs||Cornerback, Safety, Halfback||Returning||Punt returner, Kick returner|
|Receivers||Wide receiver, Tight end, Slotback||Nickelback, Dimeback||Tackling||Gunner|
|Formations (List) — Nomenclature|