What does batting 1000 mean?

Answer 1

Somebody batting a thousand had a base hit in each of his or her at bats.

Baseball statistics that call themselves percentages are generally out of 1,000, not 100. Batting average is the number of hits per thousand at bats. So somebody batting three hundred has 300 hits per 1,000 at bats, and somebody batting 1,000 has 1,000 hits per thousand at bats. Since 1941 no Major League Baseball player has ever hit over 400 in a full season.