[AtlUmpSteve]

ASA defines the infield as the area normally covered by an infielder, and the outfield as the area normally covered by the outfielders. Those definitions keep coed defenses from playing 5 infielders, or 5 outfielders; but they don't reference "the grass".

Do infielders often play on the grass? With a big LH hitter, you can betcha the 2B will be out on the grass. If they played "normal" defense, and a flare was hit to that spot 25' out into the grass, who would you expect to catch it (if it was catchable)?

If your answer is that it would be shortstop's ball, and that an infielder can play in the grass, then you have answered that this is the area normally covered by an infielder. If it is so far out that you judge it would the outfielder's ball to catch, then it is an area normally covered by an outfielder. Can't tell you at what exact distance the field changes, but the umpire has to make that call based on those factors. The ASA definitions are clearly intended to allow judgment as to what is acceptable, and not rely on where the grass starts (if it starts or ends).