It isn't fighting - nothing at all! (3,1,5)

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

'it isn't fighting nothing' is the wordplay.
I cannot quite understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
'fighting' could be 'scrap' and 'scrap' is present in the answer.
'nothing' could be 'no' (similar in meaning) and 'no' is found in the answer.
A single letter 'a' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

'at' acts as a link.

Can you help me to learn more?