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.

Unlike wide receivers, who cannot make big plays without the quarterback passing the ball to them, the running back is often given full credit for every big play he makes. Also, a running back will generally have more rushing attempts than a receiver will have receptions. Unfortunately, what most people fail to realize is that a large part of the running game relies on the offensive line.

There is a great diversity in the types of football players that play the running back position. On one extreme are smaller and agile players. One such example is Warrick Dunn, who stands at only 5 ft 8 in and weighs 185 lb, a relatively small size for a football player. These types of running backs are often referred to as "speed backs" because they rely on speed and agility to evade defenders and gain yards. At the other extreme are bigger, stronger running backs such as Jerome Bettis "The Bus", who weighs almost 260 lb (118 kg). These kinds of running backs are referred to as "power backs" because they rely on their strength and size to "truck through" defenders.

In addition to being great at running the ball, some running backs in the NFL 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. Currently there are 2 running backs on the list of the NFL's 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 LaDainian Tomlinson, who currently plays for the San Diego Chargers. 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. He also set a record by becoming the first NFL player ever to rush for over 1,000 yards and catch 100 passes in a season.