Nothing isn't a brawl! (3,1,5)

I believe the answer is:

not a scrap

I'm a little stuck... Click here to teach me more about this clue!

'brawl' is the definition.
I know nothing about this answer so I can't judge whether this works.

'nothing isn't a' is the wordplay.
I cannot really understand how this works, but
'nothing' could be 'no' (similar in meaning) and 'no' is located in the answer.
'a' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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