So gym-culture made Rocky's difficult opponent (4,8)

I believe the answer is:

ugly customer

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'rocky's difficult opponent' is the definition.
I can't judge whether this definition defines the answer.

'so gym-culture made' is the wordplay.
'made' indicates anagramming the letters.
'so'+'gym'+'culture'='sogymculture'
'sogymculture' with letters rearranged gives 'UGLY CUSTOMER'.

Can you help me to learn more?

(Other definitions for ugly customer that I've seen before include "Dangerous antagonist" , "viewed unfairly by shopkeeper?" , "Thug" , "Hard case" .)

I've seen this clue in The Telegraph.

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