Excellent youngster, foremost in Oriental martial art (6)
I believe the answer is:
aikido
'martial art' is the definition.
(aikido is a kind of martial art)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for aikido that I've seen before include "Japanese form of self-defence" , "Japanese martial art similar to judo" , "a particular form of art" , "one of the martial arts" , "Defensive moves" .)