The lag of the forearm compared to the upper arm in an overhand throw generates a large amount of stress on the elbow/UCL . I think I have read that the stress generated is actually much higher than failure stress (in tension) of the UCL (as measured in cadavers) but the surrounding muscles help in preventing a complete failure every time a pitch is thrown.
There is nothing that extreme in an UH throw…
There is lag in fastpitch as well.
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