Holy crap, it was Mike Piazza, according to the cast listing
at IMDB. I've never seen this movie, but I am a big sports fan, so I'm completely mystified that I've never heard this fact before. A very popular movie, with an eventual superstar athlete in a supporting role, and I didn't know about it? I'm really stunned that I've never heard this even mentioned over the years on SportsCenter, or wherever.
Also according to IMDB, Ron Livingston wasn't in any movies until the early '90s, so it wouldn't have been him.