Orchestra misbehave — less authentic in audition (8)
I believe the answer is:
sinfonia
'orchestra' is the definition.
(I've seen this before)
'misbehave less authentic in audition' is the wordplay.
'misbehave' becomes 'sin' (I've seen this in another clue).
'less authentic' becomes 'phonier' (I've seen this in another clue).
'in audition' shows a homophone (sound like) (audition can mean hearing).
'phonier' sounds like 'fonia'.
'sin'+'fonia'='SINFONIA'
(Other definitions for sinfonia that I've seen before include "Orchestral piece" , "Symphonic music - as if in no (anag)" , "Small orchestra" , "Without limit" , "Composition" .)