Some heretic niggles revolutionary agitator (7)
I believe the answer is:
inciter
'agitator' is the definition.
(thesaurus)
'some heretic niggles revolutionary' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'revolutionary' says the letters should be written backwards (letters revolve around).
'reticni' can be found hidden inside 'heretic niggles'.
'reticni' written backwards gives 'INCITER'.
(Other definitions for inciter that I've seen before include "provoking fellow" , "instigator of action" , "who might supply Spark?" , "He encourages" .)