And it’s bad for a kid’s arm to be teaching him a curve ball or a slider; a child’s tender young arm should not be made to twist that way.
But: consider the knuckleball.
It does not take great strength to throw it. And it does not unduly stress the arm. It’s all technique. Getting the touch. If you can teach your kid to throw the knuckleball consistently, he or she could be pitching in the major leagues till they’re 50 years old.
I’ve never heard of any young high schoolers throwing the knuckleball. They are all young and strong and generally simply want to throw as hard as they can. And the knuckleball is a tricky pitch, difficult to master. Most kids won’t have the patience. But it could be that starting in high school is just what’s needed to master the pitch. Years of study and training and practice. Dedication.
And then: unhittable.
Just think it over.
Your kid will thank you.