A proper knockout, perhaps (5)

I believe the answer is:

right

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'a proper' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for right that I've seen before include "straight" , "Equitable" , "It's what you deserve" , "The hand to the east when facing north" , "Morally good; rectify" .)

I've seen this clue in the Evening Standard.

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