Trendy rioter on the rampage inside (8)
I believe the answer is:
interior
'inside' is the definition.
('interior' can be a synonym of 'inside')
'trendy rioter on the rampage' is the wordplay.
'trendy' becomes 'in'.
'on the rampage' indicates anagramming the letters.
'rioter' is an anagram of 'terior'.
'in'+'terior'='INTERIOR'
(Other definitions for interior that I've seen before include "The area inside" , "Private" , "Inside part" , "Situated within" , "Inner part" .)