Baron and crew (4)
I believe the answer is:
band
'crew' is the definition.
(both can mean a group of people)
'baron and' is the wordplay.
'baron' becomes 'b'.
'b'+'and'='BAND'
(Other definitions for band that I've seen before include "Musicians - gang" , "Strip, belt; playing group" , "Musicians - circle" , "troop" , "Ring or musical group (4)" .)