I totally agree with Bill on this. When I was coaching the 10U/12U girls and catching some bullpen to get them warmed up, I was perplexed as to why they were calling their inside fastball a screwball. The ball just came in at different angle. Now, a curve actually curves. Btw, I hate the term back door curve in softball by the announcers. Righty pitcher throwing to a Lefty throws a curve that starts outside and ends up being a strike. And vice versa. Outside curve that comes in....that's a back door curve. Not a pitch that starts at the batter then ends up over the plate. That's called an Inside Curve. Amaright?But that's the point texasheat. 99.99999999999999% of girls that claim to have a screwball simple throw the ball inside. That's hardly a movement pitch. As I said before, if that's a movement pitch then everyone pitching in Slow-pitch throws riseballs because they throw it up high. Stepping to the left and throwing it inside is not a screwball.
Can a 2 seamer move inward? Yes. So can a 4 seamer with the right hand size and finger pressure for release. And I'd much rather have a tight spinning 4 seamer than a loose sloppy looking 2 seam that hitters can identify easier.
There are all kinds of factors that can help a ball to move. Wind, how new the ball is, and dumb luck play a role. Ever watch a 5 day match of cricket??? The ones where they wear the white uniforms, not the multi-colored ones. Anyway, you will see the bowlers (pitchers) constantly rubbing the ball on their uniform trying to shine one side of the ball so it will sway in the wind as it's thrown. Their uniforms get giant red streaks in them from the constant rubbing and shining of the ball. This can be another factor.
So, my overall problem is calling a pitch by ANY name just because it ends up somewhere. And that's what we have in most "screwballs".
Something that I never really thought about when considering the differences between softball and baseball pitches. You may have pointed this out in a different thread. Baseball pitchers tend to start the ball off the plate inside or outside and finishes over the plate. Whereas softball pitchers tend to start over the plate and end up being caught outside the zone hoping to catch an edge.