Pie is suffering from what's called testicular torsion, or, in layman's terms, a twisted testicle. It happened early in camp, but Pie had the problem reduced manually, sources said, and was able to continue playing. He was scheduled to have the corrective surgery on the Cubs off-day next Monday, but when Pie reported to camp with soreness Monday, the Cubs decided to get the procedure done today.
I am not sure I want to know how it was treated manually.
See the Cubs 2008 schedule with TV schedule at http://ignarski.tripod.com/sched2008.html