Anyone wanting to play cello with arms flailing? (9)

I believe the answer is:

allcomers

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'anyone wanting to play' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'cello with arms flailing?' is the wordplay.
'with' is a charade indicator (letters next to each other).
'flailing?' indicates an anagram (I've seen 'flailing' mean this).
'cello'+'arms'='celloarms'
'celloarms' is an anagram of 'ALLCOMERS'.

Can you help me to learn more?

I've seen this clue in The Independent.

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