Splinter group (7)
I believe the answer is:
faction
'splinter group' is the definition.
(as in a faction of an organisation)
This is all the clue.
(Other definitions for faction that I've seen before include "Act on if for a small group within a larger one" , "Clique that seeks power often through intrigue" , "Wing" , "Dissenting group within a larger one" , "group of rebels" .)