Bad stain in fabric (5)
I believe the answer is:
satin
'fabric' is the definition.
(type of fabric)
'bad stain' is the wordplay.
'bad' indicates an anagram.
'stain' is an anagram of 'SATIN'.
'in' is the link.
(Other definitions for satin that I've seen before include "Smooth and silky" , "Silk fabric" , "Smooth glossy fabric" , "Stain found in cloth" , "Shiny solk" .)