Rout about fifty in the skirmish (5)

I believe the answer is:

fight

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'skirmish' is the definition.
(I know that skirmish is a more specific form of the action fight)

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

(Other definitions for fight that I've seen before include "Spar" , "Scrap" , "Attack or engage in combat" , "Contest" , "Box" .)

I've seen this clue in the Evening Standard.

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