It's hard to knock the stuffing out of a tough one (3)

I believe the answer is:

guy

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'one' is the definition.
(thesaurus)

I don't understand how the remainder of the clue works.

(Other definitions for guy that I've seen before include "Make fun of, tent rope" , "person in shabby clothes" , "Steadying rope" , "Rope; man's name" , "Rope; man" .)

I've seen this clue in the Evening Standard.

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