pitcher throws pitch backwards

[bniu]

I was working a game the other night and with no runners on, 1-0 count, pitcher starts to pitch, well, she ended up throwing the ball backwards, as in, she "pitched" it to 2nd base. Ball just slipped from her hand as she was at the top of her windmill.

I've never seen any rule to cover that, so I just added a ball to the count and we played on. Didn't get any complaints from any coaches. Was that the correct call? What if there were runners on base?

I know in Baseball, this would be a balk, but in Softball, would this just be an illegal pitch and add a ball to the count and advance each runner one base?