A halfback, sometimes referred to as a tailback, is an offensive position in American football, which lines up in the backfield and generally is responsible for carrying the ball on running plays. Historically, from the 1870s through the 1950s, the halfback position was both an offensive and defensive position. In the related sport of Canadian football, halfback is a defensive rather than offensive position.

Before the emergence of the T-formation in the 1940s, all members of the offensive backfield were legitimate threats to run or pass the ball. Most teams used four offensive backs on every play: a quarterback, two halfbacks, and a fullback. The quarterback began each play a quarter of the way back, the halfbacks began each play side by side and halfway back, and the fullback began each play the farthest back.

The sport's first triple threat, Bradbury Robinson of St. Louis University, ran, passed, received and punted out of the halfback position. It was as a halfback that Robinson threw the first legal forward pass to teammate Jack Schneider in a game at Carroll College on September 5, 1906.

A halfback or half back may refer to:

American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football, and even more rare, the "pigskin". The ball can be advanced by running with it or throwing it to a teammate. Points can be scored by carrying the ball over the opponent's goal line, catching a pass thrown over that goal line, kicking the ball through the opponent's goal posts or tackling an opposing ball carrier in his own end zone.

In the United States, the major forms are high school football, college football and professional football. Each of these are played under slightly different rules. High school football is governed by the National Federation of State High School Associations and college football by the National Collegiate Athletic Association and National Association of Intercollegiate Athletics. The major league for professional football is the National Football League.

American(s) may refer to:

Football refers to a number of sports that involve, to varying degrees, kicking a ball with the foot to score a goal. The most popular of these sports worldwide is association football, more commonly known as just "football" or "soccer". Unqualified, the word football applies to whichever form of football is the most popular in the regional context in which the word appears, including association football, as well as American football, Australian rules football, Canadian football, Gaelic football, rugby league, rugby union and other related games. These variations of football are known as football "codes".

Various forms of "football" can be identified in history, often as popular peasant games. Contemporary codes of football can be traced back to the codification of these games at English public schools in the eighteenth and nineteenth century. The influence and power of the British Empire allowed these rules of football to spread, including to areas of British influence outside of the directly controlled Empire, though by the end of the nineteenth century, distinct regional codes were already developing: Gaelic Football, for example, deliberately incorporated the rules of local traditional football games in order to maintain their heritage. In 1888, The Football League was founded in England, becoming the first of many professional football competitions. In the twentieth century, the various codes of football have become amongst the most popular team sports in the world.