Public disorder (4)
'public disorder' 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 "Public act of violence by an unruly mob" , "Take to the streets" , "Civil unrest" , "Disturbance of the peace by many" , "Dazzling display - revelry" .)
(Other definitions for unrest that I've seen before include "Discontent verging on insurrection" , "State of turbulence" , "Feeling of anxiety or turmoil" , "State of agitation" , "Disorder" .)