Card, I once had the same problem. Used one of the splints that Rick describes and it solved the problem. I think what caused mine was a hand position I was using. I was putting my hand so far behind the ball that the back of my hand was turned in, towards my body. For me it wasn't ball weight either - I'm a pretty strong guy myself.
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Just run to the line, plant and heave.
"Things fall apart; the center cannot hold;
Mere anarchy is loosed upon the world,"