What tennis player does after a let shows modesty (7)

I believe the answer is:

reserve

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'modesty' is the definition.
(I know that modesty can be written as reserve)

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

Can you help me to learn more?

(Other definitions for reserve that I've seen before include "not in the front line" , "Lack of openness" , "Keep back - book" , "Husband - substitute" , "Modesty- store" .)

I've seen this clue in The Guardian.

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