Thug is not precise (5)
I believe the answer is:
rough
'thug' is the definition.
(both can mean a violent person)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for rough that I've seen before include "'Coarse, rugged (5)'" , "scratchy" , "Approximate - rudimentary" , "Violent type" , "Hooligan - lacking refinement" .)