Thug finding frill on Scot (7)
I believe the answer is:
ruffian
'thug' is the definition.
(I've seen this in another clue)
'frill on scot' is the wordplay.
'frill' becomes 'ruff' (a ruff is a frill worn round the neck).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'scot' becomes 'ian' (Scottish given name).
'ruff'+'ian'='RUFFIAN'
'finding' acts as a link.
(Other definitions for ruffian that I've seen before include "Lout" , "Rude fellow" , "Hoodlum" , "Yobbo" , "Violent criminal" .)