n (field sports) Any of various positions on the field of play between the forwards and the fullbacks.
n (field sports) A player who occupies one of these positions.
n (American football) An offensive back whose primary jobs are to carry the ball on running plays and to serve as a receiver or blocker on passing plays.
n (Canadian football) A defensive back whose primary jobs are to cover the slotback on passing plays and prevent running plays from going to the outside.
n (field hockey) A player in the halfback position, with both offensive and defensive roles.
n (Australian rules football) One of three players (the centre halfback and two halfback flankers) on the line between the centre line and the fullback line.
n (rugby) The player who feeds the ball into the scrum, and receives the ball as it emerges from the back of the scrum.
v To play in the position of halfback.