Female supporter rejected as vulgar (4)
I believe the answer is:
naff
'vulgar' is the definition.
(both can mean tasteless)
'female supporter rejected' is the wordplay.
'female' becomes 'f' (common abbreviation).
'supporter' becomes 'fan' (fan is a kind of supporter).
'rejected' says the letters should be written in reverse.
'f'+'fan'='ffan'
'ffan' reversed gives 'NAFF'.
'as' is the link.
(Other definitions for naff that I've seen before include "tasteless slang" , "Slangily unfashionable or rubbishy" , "common" , "Lacking taste or quality" , "Of dubious taste" .)