What a barbarian to trump a Scotsman! (7)
I believe the answer is:
ruffian
'what a barbarian' is the definition.
(thesaurus)
'trump a scotsman' is the wordplay.
'trump' becomes 'ruff' (synonyms).
'a scotsman' becomes 'ian' (common Scottish name).
'ruff'+'ian'='RUFFIAN'
'to' is the link.
(Other definitions for ruffian that I've seen before include "Hooligan" , "Lout" , "Funfair (anag)" , "Aggressive, rude troublemaker" , "Yobbo" .)