Exceptionally wide for instance (5)

I believe the answer is:

extra

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'exceptionally' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for extra that I've seen before include "Unnecessary" , "E.g. wide in cricket" , "Actor in crowd scene, no lines" , "Bit player in film" , "spotted at rear of the platoon?" .)

I've seen this clue in The Times.

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