Artist seized by girl in combat (6)
I believe the answer is:
karate
'in combat' is the definition.
(I've seen this before)
'artist seized by girl' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'seized by' is an insertion indicator.
'girl' becomes 'kate' (**).
'ra' placed into 'kate' is 'KARATE'.
(Other definitions for karate that I've seen before include "method of fighting" , "Unarmed-combat system" , "Oriental-style chops" , "Japanese form of unarmed combat" , "A Jap. martial art" .)