Definition from Wiktionary, the free dictionary
halfback (plural halfbacks)
- (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.
- (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.
- (field hockey) A position in field hockey, with both offensive and defensive roles.