Thug gets left out (4)
I believe the answer is:
lout
'thug' is the definition.
'left out' is the wordplay.
'left' becomes 'l' (common abbreviation).
'l'+'out'='LOUT'
'gets' is the link.
(Other definitions for lout that I've seen before include "A noisy, badly-behaved youth" , "thug!" , "Yahoo" , "Ill-mannered or aggressive man" , "A noisy, badly behaved youth" .)