Crossword Genius

One not easy to knock the stuffing out of (5,3)

Ross

I believe the answer is:

tough guy

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

'one not easy to knock the stuffing' is the definition.
I can't judge whether this defines the answer.

'out of' is the wordplay.
I cannot really understand how this works, but
an anagram of 'out' is 'tou' which is within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for tough guy that I've seen is " Macho man!".)

I've seen this clue in the Evening Standard.
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