Bookmaker getting new starter, this inexperienced person? (6)

I believe the answer is:

rookie

'this inexperienced person?' is the definition.
(a rookie is a new recruit or trainee)

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

(Other definitions for rookie that I've seen before include "Raw recruit" , "Army or police recruit" , "new team member" , "Slang for a new recruit" , "untested type" .)

I've seen this clue in The Times.

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