Like a judge in his garb, swapping sides (5)

I believe the answer is:

sober

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'like a judge' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for sober that I've seen before include "Dignified and sombre in manner: dry" , "Sensible - clear-headed" , "Serious - sombre" , "Restrained, grave" , "Serious or solemn and not drunk" .)

I've seen this clue in The Independent.

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