The halfback (HB) or tailback (TB) position is responsible for carrying the ball on the majority of running plays, and may frequently be used as a receiver on short (or sometimes long, depending on the system) passing plays.

What is the purpose of a fullback?

Fullbacks are typically larger than halfbacks and in most offensive schemes the fullback's duties are split among power running, pass catching, and blocking for both the quarterback and the other running back.

Is tailback the same as halfback?

The halfback's role is typically as the main ball-carrier for running plays. A tailback is simply a term for a halfback who is positioned differently at the start of the down.