He won't play second fiddle (5,6)

I believe the answer is:

first violin

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'he won't play' is the definition.
The definition suggests a singular noun which matches the answer.

'second fiddle' is the wordplay.
'second' becomes 'first' (I can't explain this - if you can you should give a lot more credence to this answer).
'fiddle' becomes 'violin' (synonyms).
'first'+'violin'='FIRST VIOLIN'

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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