Started on this thanks to Stumble Upon:
Then to here:
[www.robot-fan.net - dangit it's in japanese.
So let's check that - translated [hmm...not so good english is] for example: The robot & the fan net, "the robot ahead favorite" "this, the robot how probably will keep becoming? ?
Ok then on to google with the search term : "robot sumo wrestling"
SFGate.com has an article from six years ago [old news].
Sumo Wrestling rules - [linky]
And finally something that might be cool and relevant. Seattle Robotics Society. [linky]