You may wonder how I could call Sumo a "pure" sport, what with all the scandal the last few years. Betting on baseball, throwing bouts and the hazing of young wrestlers. Other sports have these same problems. Gambling, steroid use and other such happenings.
But lets look at the history of Sumo. Sumo wrestling like many sports was designed as a test of strength in combat. Like in the Highlands of Scotland they used these tests of strength as training for battle. You can still see this in their intense training today.
Also the religious significance is still seen today. The ritual dances take you back to an ancient time when Japan was cut off from the Western world. Watching Sumo is sort of like stepping back in time.
I think for these reasons Sumo remains a pure sport because although there have been subtle changes over the years, Sumo still retains tradition and the spirit of Japan of old.