Did athletics only start in the mid '70s or something? I wanna go deep on this one and nominate Melankomas of Caria's victory at the 207th Olympiad
as the greatest sports accomplishment in history. He was the best boxer without throwing a punch. He simply evaded his opponents until they gave up, exhausted and demoralised.
Twelve three minute rounds requires amazing stamina, and this guy apparently fought all day in the hot sun. The only possible objection is that his story may be apocryphal.