Spare one in the crowd (5)

I believe the answer is:

extra

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'spare' is the definition.
(I know that spare can be written as extra)

I don't understand the rest of the clue.

(Other definitions for extra that I've seen before include "special edition of the paper" , "Run; in addition" , "No great contribution to film" , "Taxer (anag.)" , "Bit actor in movie's crowd scenes" .)

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

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