Teams taken to be biased? (5)

I believe the answer is:

sides

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'teams' is the definition.
(eg football sides)

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

(Other definitions for sides that I've seen before include "Opposing teams or facets" , "Opposing factions or facets" , "Borders?" , "Takes the part of someone in a dispute" , "Lines" .)

I've seen this clue in the Evening Standard.

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