Bucket of balls? Think you may have undersold the Yankee's top prospect just a tad, no?
And it's possible he was hurt before, although they checked I'm sure. More likely that the M's didn't like his makup, which manifested itself in Pineda showing up for Spring Training in crappy shape. Whether he hurt himself in the off-season, or in spring training BECAUSE he wasn't in good shape, who knows.
It definitely hurts the Yankees, though. They were hoping to slot him in as a #2, maybe #3 guy, and the numbers he put up last year would have been huge. Instead they lost Montero and got a guy with crappy work ethics who now has a serious shoulder injury. Labrum isn't a good one for a pitcher, you'd rather they have Tommy John instead, as there's a documented recovery rate there, and it's a good one. Shoulder issues are harder to bounce back from.