Ruffian seen in jacket, huge (4)
I believe the answer is:
thug
'ruffian' is the definition.
(both can mean a violent person)
'in jacket huge' is the wordplay.
'in' indicates the answer is hidden within the clue.
'THUG' is hidden within 'jacket huge'.
'seen' acts as a link.
(Other definitions for thug that I've seen before include "violent gang member" , "Hooligan" , "Bully" , "Gorilla" , "Indian strangler - criminal" .)