Troublemaker (5)
(Other definitions for rebel that I've seen before include "Authority fighter" , "Anti-establishment figure" , "One refusing to conform" , "(One who) revolt(s)" , "Freedom fighter?" .)
'troublemaker' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stirrer that I've seen before include "One deliberately causing trouble" , "Spoon - agitator" , "One who spreads frightening or malicious rumours" , "engineering several revolutions in Darjeeling?" , "Scaremonger" .)