Prant-
I also agree with Joel T. Boxing may be one of the most dangerous traditional sports out there, but the debate is toughest.

There is a Native American sport that consists of 100 indians on horseback stampede down a steep hill into a huge lake once a year. Its a really sanctioned thing and all (i saw it on real TV). Many indians fall to their deaths and get trampled or drown. By your logic this Native American insanity sport would be the "toughest" because it poses a great risk of death, but by no means is it the toughest.

I'd say something that physically taxes and pushes the body to its limit is a tough sport. A triathalon, mile run, 3000m steeplechase and wrestling all are really freaking tough. When your done with the sport you've just competed in and you want to die from exhaustion, then u know its tough.