Crossword Genius

When jockeys have lost their sparkle? (4,6)

Ross

I believe the answer is:

flat racing

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

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

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

Can you help me to learn more?

(Another definition for flat racing that I've seen is " sport".)

I've seen this clue in The Irish News.
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