When I have to throw the ball slower than I normally do, I just lower it in my setup. Once you get the swing going, you won't have as much momentum, so the ball, by nature will be slower.
Just make sure that you don't, by mistake, muscle up the downswing in an attempt to throw it your normal speed or grab it at the bottom of your swing.
Just try to be loose and free.
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University at Albany 2007
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