The difference the bats/balls make.

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The most important property for softballs is compression. COR is not especially significant when multi-wall (including composites) are used. It surprises me that those 525 balls became soft. Are you sure they weren't 375 compression?

As for the Miken Ultras (I and II), banning those does make a huge difference, especially in size of sweetspot -- i.e. almost the entire bat. Miken's other bats (as well as others on the market) have much smaller sweetspots, hitting it perfectly prodices similar results as the Ultra. It just doesn't happen as often.