Sumo wrestling originated in Japan in the form of wrestling but it soon changed so that the main objective was to throw the opponent out of a ring. Samarai fighters were most likely the original wrestlers, nowadays the fighters are often reliant on body mass to force their opponents out of the ring though skill allows smaller wrestlers to compete.
The clothing worn during a fight is called the mawashi, it is made a cloth and is wrapped tightly around the body, if it falls off the opponent automatically wins.
The mawashi worn during a fight.(en.wikipedia.org)
Asashouryuu The great sumo wrestler from Darren Taylor on Vimeo
(http://vimeo.com/2029463.)
This is a quick video of a professional sumo wrestler in action, watch the way he doesn't allow the opponent to get a grip on him.
