Tail end (4)
'tail end' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stub that I've seen before include "Small piece, especially of something cut down or worn away" , "Pencil or cigarette end" , "Wee bit of pencil, eg," , "Bust (anag.)" , "Counterfoil of cheque or butt of cigarette" .)
(Other definitions for back that I've seen before include "See 12" , "part of the body" , "Support a play - player" , "ago" , "Support - defender - reverse" .)