Organise crazy trio to act violently (3,4)
I believe the answer is:
run riot
'act violently' is the definition.
(to run riot is behave violently)
'organise crazy trio' is the wordplay.
'organise' becomes 'run' (both can mean to lead or be in charge of).
'crazy' indicates anagramming the letters.
'trio' is an anagram of 'riot'.
'run'+'riot'='RUN RIOT'
'to' is the link.
(Other definitions for run riot that I've seen before include "Raise hell" , "go crazy" , "Act wildly" , "Behave unrestrainedly" , "high-scoring test match" .)