In my eyes, Boxing is the hardest. One on one combat in a very sportsman-like manner. You have to be in peak physical condition, and even then, it is such a mental game. At any time, that 'One Punch' can land just right, and you lose. If your head isn't in the right place (mentally and physically) , you lose. So many factors go into it! Speed, power, footwork, timing! Attacking on the line, off the line, in counter-time, feinting, drawing, and sheer will.

Ever try to just shadow box for a full three minutes?!? Pretty good workout. That is only one round, too. Imagine twelve three-minute rounds of that kind of activity, plus with an opponent who is punching you repeatedly in the face and stomach.

Formula 1.... you try driving at 300+ KM for +/-70 laps while pulling up to 2 or 3 Gs... definately one of the hardest sports on the planet

Scientifically Baseball is the hardest sport..

Hit a Round Ball with a round Bat square.

Out of the sports I play I'd probably say rugby would be the hardest. No padding, no throwing forward. You're constantly running, tackling and being tackled. You have to go 40 minutes before there is a break, then another 40 minutes after. Being runover with metal cleats, tackled to the ground over and over really takes it's tole on you.

golf takes the most skill

Well, I dont consider this a sport, but I think Body Building (without steroids), takes on years of dedication on developing your physique.

A true sport: Rugby must be one of the hardest sports... talk about endurance. Using your whole body: legs, arms, hands, feet. Minimal protection (no pads, just pure adrenaline).

That Tour de France sure aint no cup of tea... although Lance is making it look easy. (cough*balco*cough)