Obviously track and field is a very tough sport and all events are tough and challenging in their own regard. With that being said, what is the single hardest event in the "track" portion? I personally vote for the 400m. 400s are hard enough, but try full on sprinting a full 400. It's hell and the last 50m feels like a drag. My second vote would be for the 800 because its a hybrid event. If you're a sprinter, it's way longer than you're accustomed to and that sucks. If you're distance, you're forced to run way faster than any other distance events require. It hurts like hell for everyone.
WBU?