A halfback is an offensive position in American football, whose duties involve lining up in the backfield and carrying the ball on most rushing plays, i.e. a running back.

Why are running backs called halfbacks?

Now that most offensive formations have only one or two running backs, the original designations do not mean as much, as the fullback is now usually a lead blocker (technically a halfback), while the halfback or tailback (called such because he stands at the "tail" of the I) lines up behind the fullback.

What does halfback mean in slang?

a player stationed near the forward line to carry out chiefly offensive duties.