Playing well with telling effect (2,4)

I believe the answer is:

in form

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'playing well' is the definition.
(to be 'in form' is to be at one's best in a sport)

I don't understand the remainder of the clue.

(Other definitions for in form that I've seen before include "Fit" , "playing well" .)

I've seen this clue in The Globe and Mail.

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