Petty gangster Robin left with little hesitation (7)
I believe the answer is:
hoodlum
'petty gangster' is the definition.
(I've seen this before)
'robin left with little hesitation' is the wordplay.
'robin' becomes 'hood' (I've seen this in other clues).
'left' becomes 'l' (common abbreviation).
'with' is a charade indicator (letters next to each other).
'little hesitation' becomes 'um'.
'hood'+'l'+'um'='HOODLUM'
(Other definitions for hoodlum that I've seen before include "Person vandalising" , "Punk" , "Small-time gangster" , "Aggressive young criminal" , "Petty gangster" .)