Vulgar supporter returns at start of football (4)
I believe the answer is:
naff
'vulgar' is the definition.
(both can mean tasteless)
'supporter returns at start of football' is the wordplay.
'supporter' becomes 'fan' (fan is a kind of supporter).
'returns' says the letters should be written in reverse.
'at start of' suggests taking the first letters.
The initial letter of 'football' is 'f'.
'fan' backwards is 'naf'.
'naf'+'f'='NAFF'
(Other definitions for naff that I've seen before include "Slangily unfashionable or rubbishy" , "Vulgar, out of fashion or of poor quality" , "common" , "Lacking taste or style" , "pants" .)