In general:
I've heard that many balls don't like just sitting there, that you should rotate them every once in a while. How long has it been sitting there?
Is your apartment subject to large swings in temperature and/or humidity over the course of a day?
(There are 3 parts to most balls: coverstock, filler and core. All 3 are made of different materials. They expand and contract at different rates. If the expansion/contraction is too great, one will separate from the other. That can result in cracking.)
The other part is mistakes made by the driller in his treatment of the ball can over time results in small to large cracks: using bits that are not sharp, drilling too close to the pin, not beveling all holes, using too much super glue, etc.