Toughest, Most Physically Demanding Sport?

[Juan Bird]

Hard to believe no one mentioned Trail Running

[Maj Mujtaba]

https://www.philstar.com/entertainment/2020/06/24/2023201/philippines-freediving-sport-featured-new-netflix-series

[binsanity]

Triathlon

[snootzy]

Boxing especially if it reaches 12 rounds

[Fapuccino]

Boxing

[ilukaok]

can be broken down to contact sports or non-contact....

for contact , my vote is on boxing...

for non-contact , my vote is on hand ball.

[francis_0170]

Rugby, American Football, water polo

[Blindcorner]

Rugby and MMA UFC

[Cidex]

Rugby for me

[kawawangpinoy]

chess

[Rechsteiner]

Mostly all combat sports, especially amateur wrestling. There's a reason they have the saying "The grind is real."

[Curious Rice Porridge]

combat sports are generally taxing to your cardio 
tried jiu jitsu when i was in college, boxing now that i'm working, 
cardio is generally my achilles' heel. but on the bright it makes for a good workout

good overall body strengthening, sports climbing. 
---> stronger hands, stronger fingers... better lover

[Nicklimo]

Rugby...because they are not wearing any protective gear when playing 

[METALFREAK]

Combat Sports then American Football and Rugby

[K0RN - RETIR3D]

Spartan