Manned Humanoid Robot battles are a dead end. If you make the robots stronger, faster and more agile, you dramatically increase the chance of head injuries or deaths to the drivers. I thank the best path is autonomous Humanoid robots with some remote human override capability. Watch the movie "RealSteel" for a example of what I am talking about. The only problem with the "RealSteel' idea is the robots will be to expensive to make any robot boxing league not practical. We already have lots of smaller sized Humanoid Robot KungFu competitions like ROBO-ONE in Japan and RoboGames in California, USA. What we need to spend our money on is rescue and disaster recovery robots. Examples are the 4 meter tall humanoid robot project in Japan, the Amazon / South Korean humanoid robot called Method-2 and the robots used in the DARPA DRC (Robot Challenge) .
I personal don’t think building or promoting of large destructive robots with weapons is a good idea. Specially robots with AI. As we will be asking for trouble in so many ways.