Double-dealer turned right before a riot erupted (7)
I believe the answer is:
traitor
'double-dealer' is the definition.
(synonyms)
'turned right before a riot erupted' is the wordplay.
'turned' says the letters should be written backwards.
'right' becomes 'rt' (abbreviation as in Rt Hon- the Right Honourable).
'before' is a charade indicator (letters next to each other).
'erupted' indicates an anagram (I've seen 'erupts' mean this).
'rt' backwards is 'tr'.
'riot' anagrammed gives 'itor'.
'tr'+'a'+'itor'='TRAITOR'
(Other definitions for traitor that I've seen before include "Backstabber" , "Judas" , "Not a good subject" , "Someone guilty of treason" , "Betrayer, deceiver" .)