Group not allowed to speak? (4)
I believe the answer is:
band
'group' is the definition.
(band can mean a group of people)
'not allowed to speak?' is the wordplay.
'not allowed' becomes 'banned'.
'to speak?' indicates a 'sounds like' (homophone) clue (I've seen 'speaks' mean this).
'banned' is a homophone of 'BAND'.
(Other definitions for band that I've seen before include "troop" , "company" , "Strip, belt; playing group" , "Musicians - circle" , "A collection of musicians in ring" .)