The use of the circle is only for the look back rule.
The ump was wrong about the use of the slingshot,it is perfectly legal.I made a comment that my daughters team faced a pitcher who was 18 and a D1 signee and that her heel landed on the circle or chalk line almost every pitch, and she was leaping and no it was not called. This was summer ball in North Georgia.
She over powered our hitters and pitched a great game, how good she would be without the leap, who knows. I did not mean that she was illegal because she landed on the line if my comment has confused anyone. This young lady was very impressive, a great pitcher and I’m not trying to take anything away from her. She is well over 6 FT, if I had to guess maybe 6-4.
The only illegal pitch I’ve seen called all summer was against one of our pitchers for not pausing long enough and my daughter when she was effective mixing in the slingshot pitch with the windmill in NSA ball. We’ve tried to get them to show us where it is illegal and their answer they know it is illegal, because this coach who complained is around HS softball and he told them it was illegal. The rule says must take a windup and I’m thinking they are confusing a windup meaning a windmill motion.