A heck of a lot.
Football, soccer, cricket, baseball, ect.
it has to be out of the ordanary, an extreme sport can be anything that can put your own life at risk such as mountain biking or paintball, what makes an extreme sport is the intensity that you feel...
The same thing every other Athlete does to get better in their sport, stop being ignorant.
baseball, tennis is umpired and basketball, football, soccer, and others