Petty gangster (7)
I believe the answer is:
hoodlum
'petty gangster' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for hoodlum that I've seen before include "Petty gangster" , "Aggressive young criminal" , "Young thug or gangster" , "American thug" , "Small-time gangster" .)