Former rioter in trouble outside (8)
I believe the answer is:
exterior
'outside' is the definition.
('exterior' can be a synonym of 'outside')
'former rioter in trouble' is the wordplay.
'former' becomes 'ex'.
'in trouble' indicates anagramming the letters.
'rioter' is an anagram of 'terior'.
'ex'+'terior'='EXTERIOR'
(Other definitions for exterior that I've seen before include "Outdoor" , "Foreign" , "Face" , "Outer surface" , "Outside" .)