One reason the ball rolls over the thumb is "too" much lift with the fingers. I had a friend of mine on my team doing this and my coach made him tame his release down. This may not be the case for you guys but if it is just try to stay smooth and roll the ball...do not Rip it with your fingers.
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-If you're not willing to change, you're not willing to improve.
-Life is like a coin, you can spend it any way you want, but you can only spend it once.
-I will forever love this great game, I love the people and the competition, I only wish the best would get the recognition of an ATHLETE that they deserve.