Rogue concerned with small revolutionary groups (6)
I believe the answer is:
cadres
'revolutionary groups' is the definition.
'rogue concerned with small' is the wordplay.
'rogue' becomes 'cad' (I've seen this before).
'concerned with' becomes 're'.
'small' becomes 's' (abbreviation - e.g. clothes size).
'cad'+'re'+'s'='CADRES'
(Other definitions for cadres that I've seen before include "fighting units" , "Scared of army units" , "Inner groups of activists" , "Scared of military units" .)