barback

From bar +‎ back, due to working in the back area of the bar and not interacting with the patrons. Compare back of house and back office.

barback (plural barbacks)

1. (bartending) An assistant to a bartender.
   • 2000 December 1, Jack Helbig, “Reindeer Games”, in Chicago Reader‎^[1]:

     Cerda moved to Chicago and worked at a series of bars and clubs: the Orbit Room, the Paradise Club, even a stint at Limelight, where he supplemented his earnings as a barback by performing as Nina Hagen in one of the cages.

• runner (Britain)

barback (third-person singular simple present barbacks, present participle barbacking, simple past and past participle barbacked)

1. (intransitive) To work as a barback.

• back of house
• back office

• barback on Wikipedia.Wikipedia