Worshipper of false gods led a riot at sea (8)
I believe the answer is:
idolater
'worshipper of false gods' is the definition.
(I've seen this before)
'led a riot at sea' is the wordplay.
'at sea' indicates anagramming the letters.
'led'+'a'+'riot'='ledariot'
'ledariot' is an anagram of 'IDOLATER'.
(Other definitions for idolater that I've seen before include "Person who worships graven images" , "Heathen" , "Huge admirer" , "devotee" , "Tailored to worshipper of graven images" .)