[NoOne]

make sure to leave screen and come back to it... it may not update.. if still no change it likely does not specifically affect batting average (use "1" and "250" speed in case it's a small change as well as baserunning)

it will affect doubles/triples/singles ratio, i'd assume. it definitely matters when trying to advance runners -- not just when it pops up a window to ask, but because of that feedback we know it's part of the equation. pretty sure manual or forum post by ootp agent backs this up.

it doesn't affect defensive range / ability, as a side not of relevance

definitely affects stealing -- seems to affect quantity more than %Success, excluding clods. (latter part is from experience, not a reference / source.)

e.g. the lowest-ish speed with ~max/high stealing ability gets ~3SB maybe even 8-12SB with "1/3scale speed" a year and maintain a high % (equals > baseline average). a ~50speed guy can maintain that percentage and get quite a few more SB.

baseline steal % is one of those "averages' that actually means ~decent ability... in many aspects ~average = junk with baseball. think of the dynamics... who steals more? the guys with increased ability... significant larger quantity skews % high. if all players stole equally you'd see a much lower average-%.

every batter bats.. average = junk.