Laughfest (4)
I believe the answer is:
'laughfest' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for riot that I've seen before include "scream" , "Public act of violence by an unruly mob" , "A public affray or disturbance" , "Civil unrest" , "Violent crowd disturbance" .)