Tramp under bar, Barnaby (6)
I believe the answer is:
trudge
'tramp' is the definition.
(I know that tramp can be written as trudge)
'under bar barnaby' is the wordplay.
'under' is a charade indicator (letters next to each other).
'bar' becomes 't' (T-bar is a part of a ski lift).
'barnaby' becomes 'rudge' (Barnaby Rudge is a Dickens novel).
't' next to 'rudge' is 'TRUDGE'.
(Other definitions for trudge that I've seen before include "Plod doggedly" , "March joylessly" , "tramp" , "Walk heavily or laboriously" , "Walk wearily" .)