Little guards accompanying outlaw (6)
I believe the answer is:
bandit
'outlaw' is the definition.
(I know that bandit is a type of thief)
'little guards accompanying' is the wordplay.
'little' becomes 'bit' (a little is a bit).
'guards' means one lot of letters goes inside another (inserted letters are guarded).
'accompanying' becomes 'and' (and can mean with or accompanying).
'bit' enclosing 'and' is 'BANDIT'.
(Other definitions for bandit that I've seen before include "Violent robber" , "Member of a gang of robbers" , "Highwayman" , "Criminal type" , "Crook" .)