Crossword Genius

Spooner's cut was painful, self-inflicted discomfort (4-5)

Ross

I believe the answer is:

hair-shirt

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'spooner's' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?

I can't explain the remainder of the clue.

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I've seen this clue in The Independent.
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