Riot spray (4)
I believe the answer is:
mace
'riot spray' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mace that I've seen before include "Spice; ceremonial baton" , "put on the rack?" , "Ceremonial staff or kind of spice" , "Ceremonial staff of office" , "Disabling spray" .)