Reportedly prohibited group (4)
I believe the answer is:
band
'group' is the definition.
(band can mean a group of people)
'reportedly prohibited' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'prohibited' becomes 'banned' (banning is a kind of prohibiting).
'banned' is a homophone of 'BAND'.
(Other definitions for band that I've seen before include "Music ensemble" , "Pop group, perhaps" , "Orchestra" , "Ring or musical group (4)" , "Musicians - gang" .)