Groups involved in riots (5)
I believe the answer is:
trios
'groups involved in riots' is the definition.
'trios' can be an answer for 'groups' (I have seen 'Groups of three ' mean 'trios' so perhaps 'groups' could also mean 'trios'). I am not sure about the 'involved in riots' bit.
'involved in riots' is the wordplay.
'involved in' indicates anagramming the letters (involved can mean complex or confusing).
'riots' is an anagram of 'TRIOS'.
Can you help me to learn more?
(Other definitions for trios that I've seen before include "Works for three players" , "Groups of three" .)