On the 2nd to last game of the season, the Phillies needed a starter, and decided to let B.J. Rosenberg start what was basically a “bullpen game”. He went 4 innings, getting 12 of the 16 batters he faced out, 3 of them by strikeouts. He did walk two, but in all it was a solid outing. I am pretty sure I didn’t see him in any of his 22 relief appearances this year, so I decided to go back and watch his “start”.
Other than 14 starts in AA in 2011, Rosenberg has basically been a relief pitcher his whole minor league career (and has put up some really nice looking numbers in that time). He was drafted in the 13th round in 2008 after 4 years at college. At age 27, he just made his debut this year in the Majors. So you would think he isn’t a very interesting pitcher. However, a quick look at his velocity chart makes him at least notable.
He started off his outing with a lot of fastballs, getting up to 97 MPH (he would touch 98 MPH next inning). In the 4th, he was still hitting 97 MPH. He has averaged 94.6 MPH on his fastball this year in the Majors according to Fangraphs, with a 95.3 MPH moving fastball (Brooks Baseball calls it a sinker, it looks more like a 2-seam moving fastball to me). He mixes this with a 85 MPH slider along with a changeup. This almost looks like a starters repertoire. However, he looks more like a reliever mechanically. He brings a pretty high leg kick that may actually give him a little more deception and arches his back a little more than you would want, but the delivery looks relatively easy and non violent overall. He also throws too many balls with too many walks to be taken seriously as a starter in the Majors (although the walk rate in the minors is pretty low).
The horizontal movement of his slider sits between Andrew Cashner (99 FIP – this year with -2.4 runs on slider, but it has been positive for his career) and Manny Corpas (according to Baseball Prospectus/Brooks Baseball Leaderboard). According to vertical movement, Rosenberg is between Mike Gonzalez (77 FIP -, 1.4 run value) and Jim Henderson (50 FIP -, 2.4 run value). It usually tails out of the zone away from right-handed hitters (which seems to be the platoon he favors to throw it in, but he will throw it to lefties, and I think he needs to), but he can throw it close enough to the strike zone that you can imagine that it is enticing. The downward break is sharper than the horizontal break (which makes sense when you look at the run values and comparisons).
Overall, his fastball velocity sits between Jeremy Jeffress (98 FIP -) and Rex Brothers (74 FIP -). It doesn’t always tail, but he will occasionally tail it to either glove side or arm side. This gives him a little deception along with the velocity. He doesn’t really jam hitters with it, so it is hard to picture him breaking a lot of bats (although, perhaps ironically, he did break Sandy Leon’s bat in the 2nd inning). It also stays high, so he is going to have to rely on missing bats, as he most likely won’t get a lot of grounders (his ground-ball rate in the Majors has been terrible while his MiLB ground-ball rate was okay to average. We simply do not have a big enough sample size to look at things like whiffs/ground-balls per pitch).
The changeup was the first off-speed pitch he threw in his outing and it is a pitch he has some confidence in, throwing it 9-10% of the time since being promoted. It doesn’t have a lot of movement or life, but gives him about 10 MPH of speed differential and he can throw it for strikes. It actually moves sometimes like a 2-seam fastball at about 88-89 MPH, which would be an actual 2-seam fastball for a pitcher with slightly below average velocity. He isn’t afraid to throw it to righties, and it usually breaks in. He just needs to make sure he keeps it low, which he wasn’t always able to do.
Overall, it looks like Rosenberg has 2 MLB pitches along with a show me pitch. He has a fastball that is hard to ignore and will be 96-97 MPH (and not straight) in short spurts along with a hard slider that can break away from righties and into lefties. If in the bullpen (which is where it looks like he belongs), he won’t have to rely much on the changeup, and instead be a controllable fastball heavy reliever that can be effective and have some value for a Phillies club who could be competitive again next year.