Musicians not allowed in audition (4)
I believe the answer is:
band
'musicians' is the definition.
(I've seen this before)
'not allowed in audition' is the wordplay.
'not allowed' becomes 'banned'.
'in audition' indicates a 'sounds like' (homophone) clue (audition can mean hearing).
'banned' sounds like 'BAND'.
(Other definitions for band that I've seen before include "Belt; group of musicians" , "Group; frequency range" , "Zone; group" , "troop" , "Musicians - circle" .)