Walter, a Yankee with something handy for baseball (5)

I believe the answer is:

mitty

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'walter' is the definition.
(main character in The Secret Life of Walter Mitty)

I can't explain the remainder of the clue.

(Other definitions for mitty that I've seen before include "Walter --, Thurber's daydreaming hero" , "Walter ---, Thurber's fantasist" .)

I've seen this clue in the Evening Standard.

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