This game uses I believe the C5161-1 batting unit with a metal bat that the linked charts say uses a 7/8" ball. The charts also indicate a 4693 pitching unit the same as the previous year game Four Bagger.
AlexF, has a great example of that game and is very helpful. He usually answers here. If you want PM him and he will tell you the number of balls he has in his game and confirm it is a 7/8" ball.