[quote=“KreGg”]Hmm thanks for the explanation Roger.
And by the way, which would be the most stressful pitch? Slider? Splitter? Sinker? Curve?[/quote]
The quick answer to your question is, while all of the pitches you listed can be thrown improperly such that the all can be stressful on the arm, the slider is generally the most stressful.
Any pitch thrown with pronation (e.g. the change-up, sinker and screwball) should be safe because all rotation of the hand/wrist/forearm is in the same direction the hand/wrist rotate after release of the ball. Plus, force is imparted around the ball so less force is applied to the arm.
Pitches thrown with a twist during forward acceleration of the arm are the most stressful because the hand/wrist/forearm rotate the opposite direction as the upper arm and because there is an abrupt change of direction of the hand/wrist/forearm once the ball is released. (The arm always pronates after the ball is released regardless of which pitch was thrown.) Examples here include all improperly thrown breaking balls. The slider is the worst because in involved the most force on the arm as well.
Pitches thrown with supination that is set before forward acceleration begins such that there is no further twist are closer to the safe side of things so long as their numbers are also limited. Examples of this include all properly thrown breaking pitches. But the slider is still the worst because, again, it puts the most force in the arm.
Some pitches thrown with supination create more of a tendancy to further supinate during forward acceleration than others so these are more risky to throw. The slider is the prime example of this but I’d also include the cutter and slurve.
The splitter is unsafe only if you supinate during forward acceleration. According to Tom House, this happens when you let your thumb creep up the side of the ball towards the index finger. Keep the thumb centered below the “V” formed by the index and middle fingers and you’ll have less of a tendency to twist.