Running back

A running back (RB) is the position of a player on a 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 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 running backs, with a lot of carries, will have 30 rushing attempts, while receivers, with a lot of yards, 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.