Halfback/tailback
The halfback or tailback 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.
Read more about this topic: Running Back