Did it have a flat spot when it was drilled?
If not, maybe it got chipped when it hit something at the backstop? Balls often hit nails and pieces and get cracked that way. I've had two recent polyester balls crack right around the bridge when it hit something sticking out back there. Once a piece chipped off, it is probably easy for stress fractures to follow.
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"None are so blind as those who will not see."