Uprising overblown in English county seat (8)

I believe the answer is:

buttocks

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'seat' is the definition.
(I know that seat can be written as buttocks)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for buttocks that I've seen before include "Body parts covered at least by 13" , "Get behind" , "Sit on them" , "Bottom" , "Rear" .)

I've seen this clue in The Guardian.

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