I don't know if any of these counts, but because I had a kid who was into speedskating, I saw Bonnie Blair practicing, from right next to the track at the Petitt Center, and Shani Davis winning a lot of pack-style races with other kids. Also Beth Heiden skating with a local club.
Who is the best athlete relative to their sport you saw play live?
I'm gonna say Mia Hamm at the 1996 Olympics.