Crossword Genius

What's left for attack following trap (3,6)

Ross

I believe the answer is:

net profit

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

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

'for attack following trap' is the wordplay.
'for' becomes 'pro' (I've seen this before).
'attack' becomes 'fit' (fit is a kind of attack**).
'following' means one lot of letters go next to another.
'trap' becomes 'net' (net is a kind of trap).
'pro'+'fit'='profit'
'profit' put after 'net' is 'NET PROFIT'.

Can you help me to learn more?

(Other definitions for net profit that I've seen before include "Excess of sales over costs for potent fir" , "Actual money to be made" , "Earnings after all deductions" , "return from business" , "What's finally made" .)

I've seen this clue in The Telegraph.
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