Crossword Genius

Champion rugby player's single set of books (9)

Ross

I believe the answer is:

proponent

'champion' is the definition.
(thesaurus)

'rugby player's single set of books' is the wordplay.
'rugby player' becomes 'prop' (I've seen this in other clues).
'single' becomes 'one' (I've seen this before).
'set of books' becomes 'nt' (New Testament).
'prop'+'one'+'nt'='PROPONENT'

(Another definition for proponent that I've seen is " Advocate (of a theory, etc)".)

I've seen this clue in The Telegraph.
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