Unlikely trio engage in boisterous activity (4)

I believe the answer is:

riot

I'm a little stuck... Click here to teach me more about this clue!

'activity' is the definition.
(riot is a kind of activity)

'unlikely trio engage in boisterous' is the wordplay.
'trio' can be anagrammed to 'RIOT'.
However, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for riot that I've seen before include "Disturbance by unruly mob" , "Dazzling display - revelry" , "Crowd violence" , "Public disorder" , "Wild revelry" .)

I've seen this clue in The Irish Times.

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