A number holding promotion by pub is shabby (10)
I believe the answer is:
threadbare
'shabby' is the definition.
(I've seen this before)
'a number holding promotion by pub' is the wordplay.
'a number' becomes 'three' (three is a number).
'holding' means one lot of letters goes inside another.
'promotion' becomes 'ad' (short for advert).
'by' means one lot of letters go next to another.
'pub' becomes 'bar' (both are drinking establishments).
'ad'+'bar'='adbar'
'three' placed around 'adbar' is 'THREADBARE'.
'is' acts as a link.
(Other definitions for threadbare that I've seen before include "Tired" , "the worse for wear" , "cliche-ridden" , "Thin, tattered, worn out" , "Shabby" .)