Parkour or Yamikasi, or real people who want to be urban Ninjas. This just proves that you can have a real life Naruto or Kenshin - the thought is kind of awesome.

Wiki is awesome:
Parkour
Yamakasi

This is the type of sport that I can watch all day. Especially if they stylise it slightly like they do for the soft drink ads (for the life of me I can't remember what brand they were advertising for).

The thing is - this actually makes me believe they can make a life action Naruto film that won't be completely dependent on special effects and heavily edited fight scenes.