It's worrying when an unruly gang is out to succeed (7)

I believe the answer is:

gnawing

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'it's worrying when' is the definition.
I can't judge whether this defines the answer.

'unruly gang is out to succeed' is the wordplay.
'unruly' indicates anagramming the letters.
'is out' indicates putting letters inside.
'to succeed' becomes 'win' (succeed can mean to win or excel).
'gang' with letters rearranged gives 'gnag'.
'gnag' going around 'win' is 'GNAWING'.

'an' acts as a link.

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