Let me start off by saying I was wrong about Rosin. I thought that he was a bullpen piece all the way and so far he has gone a long way to proving other wise.
How We Got Here:
Rosin was a 2010 4th round pick by the San Francisco Giants out of the University of Minnesota. In college his fastball worked 91-92 touching 94, though the summer before he touched 96 on the Cape. His secondary offering were fringy and most scouts thought he belonged in the bullpen possibly in a high leverage role. The Giants moved him to the bullpen part time after drafting him, but after acquiring him in the Hunter Pence trade the Phillies moved him back to the rotation.
The fastball usually sits 90-91 but he gotten stronger deeper into games sitting more around 93 in later innings (at times touching as high as 95). The slider has progressed to at least an average pitch and the changeup might eventually reach average. The raw stuff plays up because Rosin can consistently throw it for strikes and from his large frame he can get good plane on his pitches. Rosin has a large frame that suggests he can be a workhorse out of the rotation and he has started to prove that not only can he keep velocity but he can add some too over a game.
Rosin is not over powering but he will strikeout his share of batters. The biggest thing is that he does not walk very many batters. If you take away his start on May 15 when he walked 5 batters Rosin has walked 6 batters over 47.1 IP good for a 1.14 BB/9.
Where does it go from here:
If Rosin can just keep the velocity up and the walks down he is a back of the rotation starter. He lacks a true overpowering pitch to make the profile better and at 24 years old most of the projection is gone. But if Rosin can be a #4 starter that is a great return for the third man in the Hunter Pence trade. If the changeup cannot continue to trend upwards then Rosin could end up back in the bullpen where the fastball slider combination could make him an above average reliever.
Rosin will need to be protected after this year which makes him an interesting starting candidate for the big league club if Morgan, Martin, Cloyd, and Biddle continue to struggle with injuries and inconsistencies.