Consider today's column my personal testimony that the sport of sumo can be a very useful aid for learning the Japanese language.
I suppose most of us first encounter sumo on NHK TV's daily broadcasts of the six annual 本場所 (honbasho, main tournaments). It's not difficult to pick up new vocabulary just by listening to the commentary and interviews. By reading the テロップ (teroppu, subtitles or captions) flashed on the screen, you can also easily acquire new kanji, starting with the 四股名 (shiko-na, professional names) of the competitors and their win-loss record.
Along with the sports newspapers, sumo is also covered in depth by several bimonthly periodicals. Spend some time reading these, and before you know it you'll be able to recognize the wrestlers' personalities and appreciate their various techniques.