Listener in agreement with unrestrained person (11)

I believe the answer is:

concertgoer

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'listener in agreement' is the definition.
The definition suggests a singular noun which matches the answer.

'with unrestrained person' is the wordplay.
'with unrestrained' becomes 'concert' (I can't justify this - if you can you should believe this answer much more).
'person' becomes 'goer' (goer is a kind of person).
'concert'+'goer'='CONCERTGOER'

Can you help me to learn more?

(Another definition for concertgoer that I've seen is " Eg, prommer".)

I've seen this clue in The Daily Express.

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