Combat sport (6)
I believe the answer is:
karate
'combat sport' is the definition.
(I know that karate is a type of martial arts)
This is the entire clue.
(Other definitions for karate that I've seen before include "Japanese martial art" , "SPORT/GAME" , "method of fighting" , "Martial art (with chopping?)" , "A Jap. martial art" .)