Tastelessly loud supporter’s disheartened, say (6)
I believe the answer is:
brassy
'tastelessly loud' is the definition.
(I've seen this before)
'supporter's disheartened say' is the wordplay.
'supporter's' becomes 'bras'.
'disheartened' suggests removing the centre.
'say' with its middle taken out is 'sy'.
'bras'+'sy'='BRASSY'
(Other definitions for brassy that I've seen before include "Sounding like cornet maybe" , "club" , "Showy - harsh" , "Insolent" , "Bold and vulgar like yellow metal" .)