rosy:
shake your head all you want. Most times an arm that is unable to throw a baseball with great velocity is still a very functional arm for all the things needed in day-to-day life.
If I'm a kid with average ability and I know that this is my time in the sun, then I'll throw curve balls until my arm falls off.
And, I bet, nearly every time there is no lasting injury anyway.
If I'm a stud (and by 12 you have a pretty good sense) then I probably won't throw the curve.
Have a swell time shaking your head.