Any sport. And use “witnessed” as liberally as possible. In person, a participant, on TV, listening to the radio, streaming, whatever. It just has to be something that left an indelible impression on you. I’ll be happy to start.
I watched the 1973 Belmont Stakes only because Secretariat was trying for the Triple Crown. I know nothing about horse racing, and don’t even like horses. But when I saw Secretariat, well, I know an athlete when I see one … even if it has 4 legs instead of 2. What that horse did in that 2-1/2 minutes was the most extraordinary athletic performance I ever saw. It was the equivalent of Jim Brown rushing for 400 yds., or Babe Ruth hitting 6 homers in a game. It was spellbinding to watch. And I can still see that Big Red pile of muscle basically lapping the field. Gave me chills, knowing I was watching something that was absolutely unique.