Apparently, after his initial physical this spring the doctors concluded he had one of the top 3 strongest shoulder on the team after his offseason workout program. The guy wants to close and he made that clear to the team, so they're going to go with it. If it is where he wants to be one can't really fault the team for putting him back there. While I was curious to see how good he would be in the rotation, it is probably best for the team to have him at the end of games. Plus he was a joy to watch in that role. I don't see Tavarez lasting the year as a starter but they have Lester once he's ready, Kason Gabbard looked good last year in a few spot starts and has looked awesome this spring, and there's always the possibility of a Rocket-Relaunch (though admittedly that isn't likely).
We'll all have to wait and see how it plays out. Certainly there's a risk for injury but there would be for him as a starter too. Pitching is such an inexact science, no one knows for sure what is best for pitchers. Just look at the different philosophies between the Japanese pitchers and American ones for evidence of that. If they didn't think he could remain healthy they wouldn't be putting him in this position. It is in the best interests for the club to have Papelbon pitching for a long time for their team so they'll keep a close eye on him.
Comment