So, when that day comes I should have my dd learn a generous step to the left?The point of the leap left is the smoke and mirrors tied to the screwball. Make the batter think an outside pitch is coming, but hit the inside corner. The batter will usually either take the pitch for a strike (assuming the umpire is liberal on the inside, because they're fooled just as much as the batter), or the batter will reach a bit and hit into an easy out or foul off the handle of the bat.
I do believe that screwballs, when the proper spin is imparted on the ball, do drift or curve a bit. The good ones are not thrown straight, however, they do not "break", where a "break" defines late or sudden movement. Hell, anyone who has ever stood on a field with softball players and caught balls during infield practice knows that ball that travels straight is more of a rarity the a ball that curves or drifts
-W