Go off, suppressing onset of imminent scream (4)
I believe the answer is:
riot
'scream' is the definition.
(I've seen this before)
'go off suppressing onset of imminent' is the wordplay.
'go off' becomes 'rot' (I've seen this before).
'suppressing' is an insertion indicator.
'onset of' says to take the initial letters.
The initial letter of 'imminent' is 'i'.
'rot' going around 'i' is 'RIOT'.
(Other definitions for riot that I've seen before include "A wild public affray" , "Disturbance of the peace by many" , "Debauchery" , "Violent disturnance of the peace (by crowd)" , "Crowd violence" .)