Japanese sport (6)
'japanese sport' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sumo that I've seen before include "Type of Japanese wrestling" , "Japanese wrestling sport of over-weight men" , "Japanese form of wrestling" , "Japanese wrestling with big fat men" , "foreign form of fighting" .)
(Other definitions for karate that I've seen before include "Japanese form of unarmed combat" , "Japanese martial art" , "Japanese art of unarmed combat" , "A taker (anag)" , "method of fighting" .)