Newcomer's music upset audience finally leaving concert hall, say (7)
I believe the answer is:
parvenu
'newcomer's' is the definition.
(I've seen this before)
'music upset audience finally leaving concert hall say' is the wordplay.
I cannot quite see how this works, but
'music' could be 'par' (I have seen 'Black music' mean 'par' so perhaps 'music' could also mean 'par') and 'par' is located in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for parvenu that I've seen before include "An upstart, new arrival to society" , "One newly risen to wealth or power" , "One who climbs" , "Johnny-come-lately, upstart" , "Arriviste" .)