Bitter civil riot erupting (9)
I believe the answer is:
vitriolic
'bitter' is the definition.
(synonyms)
'civil riot erupting' is the wordplay.
'erupting' indicates anagramming the letters.
'civil'+'riot'='civilriot'
'civilriot' is an anagram of 'VITRIOLIC'.
(Other definitions for vitriolic that I've seen before include "Scathing" , "Highly corrosive" , "Cruelly savage (criticism)" , "harsh" , "Filled with malice" .)