Sporting chance without scratching what the swingers enjoy (4)

I believe the answer is:

open

I'm a little stuck... Click here to teach me more about this clue!

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

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for open that I've seen before include "Frank; unobstructed" , "Allowing entry and exit" , "Release" , "Uncovered" , "Frank - unsettled" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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