A riotous engagement (5)

I believe the answer is:

melee

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'a riotous engagement' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe there's an association between them I don't understand?

This is the entire clue.

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(Other definitions for melee that I've seen before include "Skirmish" , "Noisy riotous fight" , "A confused free-for-all" , "Rumpus" , "A confused fight or muddle" .)

I've seen this clue in the Evening Standard.

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