Not against a professional (3)

I believe the answer is:

pro

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'professional' is the definition.
(abbreviation)

I don't understand the rest of the clue.

(Other definitions for pro that I've seen before include "Favouring the professional" , "Professional; advantage" , "Paid worker" , "Of argument, say, in favour of" , "For; non-amateur" .)

I've seen this clue in The Globe and Mail.

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