Crowd disturbance, uproar (4)
I believe the answer is:
riot
I believe this clue is a double definition.
'crowd disturbance' is the first definition.
(I've seen this in another clue)
'uproar' is the second definition.
(both can mean a disturbance or commotion)
(Other definitions for riot that I've seen before include "Public act of violence by an unruly mob" , "Violent disturbance by mob" , "The unruly may run this" , "unrestrained revelry" , "Civil disturbance" .)