It was a few years ago, and it was at the AAA level, but I spent several summers working as a stringer for BIS. Greatest part time job ever...paid to watch baseball. At that time, at that level, there was no video, each game had two stringers and we charted each ball in play as it happened live. As far as I know, we all put some effort into getting it right, but it was still pretty haphazard. I'm sure at the big league level it's much more accurate. Sadly, I had to give it up when my real job got in the way, and now that I could do it again, we no longer have a AAA team in Tucson.