Free fight in horse’s compartment (8)

I believe the answer is:

loosebox

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'horse's compartment' is the definition.
The definition suggests a singular noun which matches the answer.

'free fight' is the wordplay.
'free' becomes 'loose' (similar in meaning).
'fight' becomes 'box' (boxing is a kind of fighting).
'loose'+'box'='LOOSEBOX'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for loosebox that I've seen before include "Quarters" , "Stall for horse" .)

I've seen this clue in The Times.

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