1) Back 2) Ball-carrying player 3) Ballcarrier 4) Offensive football position 5) Queue of traffic 6) The person who plays tailback 
An offensive player who runs with the football.
The running back deepest from the offensive line. Usually the team
player position on offense farthest ('deepest') back, except in kicking formations. Also often referred to as the running back, particularly in a one-back offense.