Musician to prohibit supporter? (8)
I believe the answer is:
banjoist
'musician' is the definition.
(I know that banjoist is a type of musician)
'prohibit supporter?' is the wordplay.
'prohibit' becomes 'ban' (banning is a kind of prohibiting).
'supporter?' becomes 'joist' (something which supports a building's structure).
'ban'+'joist'='BANJOIST'
'to' acts as a link.
(Other definitions for banjoist that I've seen before include "Musician" , "plucky performer" , "Player of stringed instrument" , "plucky player" .)