Running back
A running back (RB) is the position of a player on an American and Canadian football team who lines up in the offensive backfield. Depending on the offensive formation, there may be one or two (or strictily speaking three on the field - see fullback below. A running back may be a halfback (or half back), tail back, slotback, (or strictly speaking a full back) depending on the formation.
Halfback, tailback or running back
The halfback or tailback position is one of the more glamorous positions on the field, and is commonly viewed as a requirement for a team's success. They are responsible for carrying the ball on the majority of running plays, and may frequently be used as a receiver on short passing plays. 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. On some rare occasions, running backs are used to pass the ball on a halfback option play or halfback pass.
No position in 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 play), the running back 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. This is mainly because, in a reception, a receiver will average, generally, from 10 to 20 yards, which is 2 to 4 times the average of a, good, 5 yard run. That's why runningbacks ,with a lot of carries, will have 30 rushing attempts, while receivers, with a lot of catches, will have 10 receptions. A large part of the running game relies on the offensive line, which must block for the running back, providing him with holes in the defense to run through.
Fullback
In the college and professional ranks, fullbacks carry the ball infrequently. Currently, they are primarily used to aid the offensive linemen in blocking. On most running plays, the fullback leads the halfback, attempting to block potential tacklers before they reach the ball carrier. Also, fullbacks are sometimes used in passing plays, although they typically protect the quarterback. Fullbacks are technically running backs, but today the term is usually used in referring to the halfback or tailback. Although fullbacks currently are rarely used as ball carriers, there was once a time when they ran the ball as frequently as running backs. In high school football, where the offenses are more simple and player sizes vary greatly, fullbacks are still frequently used as ball carriers.
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. There have been some exceptions, however. Mike Alstott of the Tampa Bay Buccaneers often carries the ball and is also used as a receiver in short pass situations. Fullbacks are also still used occasionally as rushers on plays when a short gain is needed for a first-down, as they are large and powerful and therefore good for breaking through the line for a short distance.
Characteristics of a running back
Height
There is a great diversity in those who play at the running back position. At one extreme are smaller, agile players, such as Barry Sanders, who stood at only 5 ft 8 in, and Maurice Jones-Drew, at 5 ft 6 in. These running backs are usually scat backs, or fast, elusive running backs. However, Maurice Jones-Drew is also known for his powerful running style in addition to his speed, despite his height. At the other extreme are bigger, stronger players, such as Jerome Bettis, "The Bus", who, at his retirement in 2006 weighed almost 260 lb (118 kg). This kind of running back is referred to as a "power back" because they rely on their strength and size to break through defenders. They are usually slow, compared to most NFL players, and usually do not run to the outside, instead opting to run through the line. They must also be able to protect the ball well. Most successful running backs fall somewhere between these extremes, combining speed with power, such as Walter Payton.
Receiving ability
In addition to skill at running the ball, some running backs in the National Football League are known for their prowess at catching passes. The role of the running back as a receiver out of the backfield has expanded greatly in the NFL over the years, and a versatile running back who provides his team good running and pass-catching abilities is highly valued. On passing plays, a running back will often run a safe route, such as a hook, creating a safe target for a quarterback to throw to if all other receivers are covered. The increase in demand for running backs with good receiving abilities can be attributed to the rise in popularity of the West Coast offense and its variants, which often requires its running backs to catch passes on a regular basis. Currently there are two running backs on the NFL's list of all-time top 20 leading pass catchers, fullback Larry Centers and halfback Marshall Faulk. A good example of a dual threat running and pass catching running back is San Diego Chargers' LaDainian Tomlinson; in 2003, Tomlinson rushed for 1,645 yards and caught 100 passes for 725 yards, giving him 2,370 total yards from the line of scrimmage, and he became the first NFL player ever to rush for over 1,000 yards and catch 100 passes in a season.
Some teams have a running back known as the "third down back", who is more skilled at catching passes than the starting running back on the team, and thus is often put in the game in third down and long situations where a pass is needed to pick up a first down, and/or is better at pass blocking or "picking up the blitz" than than the other backs as the running back is typically asked to block on passing downs. 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.
Blocking
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, such as Lorenzo Neal, are usually key components for a running back's success (as seen in Ladainian Tomlinson's record-breaking season in 2006).
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 1 or 2 yards to get a first down. 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 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 players that are being blocked without dropping the ball.
Kick and punt returners
Another duty of a running back is returning punts and kickoffs on special teams. Although this is most often done by wide receivers and defensive backs (because they are generally the fastest players on the team), some running backs have enough speed and talent to perform this role. The NFL's current all time leading in kickoff return yards (14,014 yards) and punt return yards (4,999) is a running back, Brian Mitchell. He also gained 1,967 rushing yards, 2,336 receiving yards, and 15 fumble return yards, giving him a total of 23,330 all-purpose yards, the second most in NFL history behind Jerry Rice.