UFC and boxing are both goddamn hardcore, and even most of the more 'respectable' martial arts are pretty intensive at competition level (Muay Thai is brutal.).

However, there's a difference between 'most intensive' and 'works hardest'. I'm sure that most sportsmen - be they players of soccer, cricket, basketball, hockey, whatever - work extremely hard to be at their best, and even though I'm not big into sports I'm not about to claim players are untalented or don't invest a lot of effort.

Jai Alai is pretty rough, too. That thing can top 180mph.

Of course, we can't really compete today with Mesoamerican Ball. Sometimes the losing team was sacrificed. At times, the winning team was deified through decapitation by the losing team, too. And on occasion the skulls were as the base for more balls to be made.