Unmanageable mob or tumultuous trio (4)
I believe the answer is:
riot
'unmanageable mob' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'tumultuous trio' is the wordplay.
'tumultuous' indicates anagramming the letters.
'trio' is an anagram of 'RIOT'.
'or' acts as a link.
Can you help me to learn more?
(Other definitions for riot that I've seen before include "Public act of violence by an unruly mob" , "very funny" , "Uprising" , "Public disorder" , "Run amok" .)