Only a beginner in horse racing? (7)

I believe the answer is:

starter

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'beginner in horse racing?' is the definition.
'starter' can be an answer for 'beginner' (starter is a kind of beginner). I am not sure about the 'in horse racing?' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for starter that I've seen before include "No substitute" , "Appetiser" , "Beginner, or opening course of meal" , "Race gun firer" , "Hors d'oeuvre" .)

I've seen this clue in the Evening Standard.

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