It’s no great revelation to say that working the corners by being able to hit your spots inside and outside is a critical skill for fastpitch softball pitchers. The easiest pitches to hit are the ones down the middle, so once you can do that reliably the next step is learning to never throw there again (except maybe on a 3-0 count).
Of course, it’s easy to say “you have to hit your spots.” It’s another thing for fastpitch pitchers, especially younger ones, to be able to do it.
There are a lot of moving parts involved in fastpitch pitching, and going inside and outside reliably requires being able to make fine motor adjustments. Not every pitcher is able to do that on-command.
So with that in mind, here’s a quick video blog that shows a drill to help pitchers get the concept of making adjustments by starting broader and working their way back in. The drill will work no matter what technique you use to throw inside/outside.
It’s being demonstrated with an outside curve ball, by the way, but it will work for any pitch.