Violent criminal (4)
'violent criminal' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ruffian that I've seen before include "Hoodlum" , "Violent, lawless person" , "Hooligan" , "Funfair (anag)" , "Thug" .)
(Other definitions for hoodlum that I've seen before include "Aggressive young criminal" , "Person vandalising" , "Small-time criminal" , "Young thug or criminal" , "American thug" .)
(Other definitions for gangster that I've seen before include "Villain" , "Mobster" , "Typical Cagney role" , "Member of a mob like Al Capone" , "Hoodlum" .)
'violent criminal' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thug that I've seen before include "16 21 [INDIAN IMPORT]" , "A vicious or brutal ruffian" , "Violent hoodlum" , "Violent lout" , "Rough" .)