True story: One of the first Baseball Prospectus events I ever did was at a Giordano's in Chicago back in 2003. It was Rany Jazayerli, Nate Silver and myself. (What ever became of those guys anyway?) During the Q&A, someone asked a question about a young Phillies prospect. Rany, then the resident prospect guru, gave his opinion, but because of his pre-draft medical issues, I was asked my opinion on Cole Hamels.
"A left-handed Mark Prior," was my reply. At the time, in Chicago, that was one heck of a compliment.
Prior went on to have a nice year in '03, but a fluke injury took him down. Hamels, on the other hand, went on to become one of the best lefty pitchers in baseball over the last decade. Now, Hamels is having a minor shoulder problem of his own.
Hamels reported to spring training and promptly told reporters, per the Associated Press (via Yahoo! Sports), he was a week behind schedule. During the offseason, Hamels suffered through a bout of tendinitis in his shoulder. This is not uncommon for pitchers, and the standard of care is normally to take a look, make sure that there's nothing more wrong with the shoulder and then to use rest to allow the inflammation to calm down.
There's no evidence that Hamels needed anything more serious than rest and likely some anti-inflammatories to clear it up. At this point, Hamels does not appear to be injured, just behind schedule.
Pitchers are usually on very strict schedules for offseason throwing and the buildup to the season. Spring training allows pitchers to "stretch out" their arms over several starts, increasing their stamina to be ready for April, not mid-February. That traditional schedule is the reason pitchers and catchers report early.
Remember that Hamels is perhaps the best example of a modern Tom House pitcher. The former Rangers pitching coach now consults with many, especially young pitchers, and in this era, few have been more touted than Prior and Hamels. Hamels' fluid mechanics and linearity have allowed him to overcome a heavy workload during his pre- and post-age-25 seasons.
Hamels is hardly the only pitcher to encounter offseason issues. Jeremy Hellickson had elbow surgery, and many others—lower-profile pitchers—will find themselves behind schedule in days or weeks. While the pitching motion itself is not unnatural, it's the repetitive nature of the position that puts serious demands on the various joints, muscles and connective tissue.
The question now is whether Hamels is actually a week or so behind schedule. We'll know quickly as spring training gets under way. If Hamels does miss his first scheduled start or is an inning or so behind his teammates—including new Phillie A.J. Burnett—we'll know that head athletic trainer Scott Sheridan and his staff have things under control. If it's more, Ryne Sandberg has his first challenge as manager.