Home supporter hears groups of people fighting (10)

I believe the answer is:

infantries

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'groups of people fighting' is the definition.
The answer and definition can be both groups as well as being plural nouns.
Maybe there's a link between them I don't understand?

'home supporter hears' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'supporter' becomes 'fan' (fan is a kind of supporter).
'hears' becomes 'tries' (to try or hear in the legal sense).
'in'+'fan'+'tries'='INFANTRIES'

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I've seen this clue in The Guardian.

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