Pop group forbidden on the radio (4)
I believe the answer is:
band
'pop group' is the definition.
(I've seen this before)
'forbidden on the radio' is the wordplay.
'forbidden' becomes 'banned' (banning is a kind of forbidding).
'on the radio' shows a homophone (sound like).
'banned' is a homophone of 'BAND'.
(Other definitions for band that I've seen before include "Belt; group of musicians" , "A collection of musicians in ring" , "Musicians - circle" , "Ring or musical group (4)" , "Strip, belt; playing group" .)