When pitches cross the plate in the shadow zone, they are between the heart of the plate (predominantly strikes) and the chase zone. Whether the batter swings, or doesn’t swing, pitches in that zone have uncertain outcomes. If a batter can dominate that zone, likely he will be successful.
Ben Clemens wrote Low and Away Crushes Lefties. Mostly at Least. He combined 2019 and 2020 data. He looked at pitches that crossed the plate in a specific 6” by 8” rectangle, roughly equivalent to Baseball Savant’s shadow zone 17. Let’s call zone 17 the Darkest Shadow Zone.