Fullback is one of the positions in a rugby league football team. Typically wearing jersey number 1, the fullback is a member of the team's 'back-line'. The position's name comes from their duty of standing the furthest back in defence, behind the forwards (8-13), half backs and the three-quarter backs (2-5). Fullbacks are therefore the last line of defence, having to tackle any opposition players and regather the ball from any kicks that make it through their teammates. It is for this reason that the fullback is also referred to as the sweeper or custodian. Being able to secure high bomb kicks is a highly sought quality in fullbacks.

Rugby league football, commonly known as rugby league in English-speaking countries and rugby XIII in non-Anglophone Europe and South America, and referred to colloquially as rugby, football, footy or league in its heartlands, is a full-contact sport played by two teams of thirteen players on a rectangular field measuring 68 m (74 yd) wide and 112–122 m (122–133 yd) long with H-shaped posts at both ends. It is one of the two major codes of rugby football, the other being rugby union. It originated in 1895 in Huddersfield, Yorkshire, England, as the result of a split from the Rugby Football Union (RFU) over the issue of payments to players. The rules of the game governed by the new Northern Rugby Football Union progressively changed from those of the RFU with the specific aim of producing a faster and more entertaining game to appeal to spectators, on whose income the new organisation and its members depended.