Crossword Genius

Marksman hits too randomly after onset of short-sightedness (8)

Ross

I believe the answer is:

shootist

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'marksman' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I can't see?

I cannot understand how the remainder of the clue works.

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I've seen this clue in The Times and The Sunday Times.
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