Prison agitation (4)
I believe the answer is:
stir
I believe this clue is a double definition.
'prison' is the first definition.
(informal term for prison)
'agitation' is the second definition.
(in the sense of a disturbance)
(Other definitions for stir that I've seen before include "Whisk or rotate" , "Prison (sl.); agitate" , "Prison (slang) - disturbance" , "Begin to move" , "riot" .)