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' is the definition.
I can't tell whether this defines the answer.

'an unruly gang is out to succeed' is the wordplay.
'an unruly' indicates anagramming the letters.
'is out' means one lot of letters goes inside another.
'to succeed' becomes 'win' (I've seen this in another clue).
'gang' is an anagram of 'gnag'.
'gnag' enclosing 'win' is 'GNAWING'.

'when' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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