Here’s Ben over at RAB on Joba’s latest start:
For Joba, the problem seemed to be one of velocity. While he was throwing more strikes, he averaged below 92 with his fastball and peaked at around 94.4. His changeup, slider and curve were all working nicely, but I still wonder, as I have many times this season, where Joba’s 97 mph fastball went. He threw it last year regularly as a starter but only occasionally this year.
Now here are some interesting numbers on Joba’s fastball via FanGraphs:

From 2007-2008, Joba famously started as a reliever and he then transitioned into the rotation in ’08. Therefore, the velocity on his fastball during those years is somewhat inflated. This season, Joba is a full-time starter and we’ve seen a noticeable drop in velocity. That is to be expected, of course. However, as Ben notes, Joba’s dominant heat—the velocity he brought to the table last year as a starter—has all but vanished. Obviously, it’s okay to conserve one’s energy and save the gas so that you can go deep into ballgames, but Joba’s fastball is an entirely different animal this season (there’s no premium gas). In fact, due to newly his tamed fastball, Joba has seriously suffered as a starter in 2009.
According to FanGraphs’ pitch value data, Joba’s fastball is worth 15 runs below average. That’s third worst in the AL behind Detroit’s own, Armando Galarraga and our old friend, Carl Pavano. In 2008, when Joba’s fastball still popped as a starter, the pitch was 8.6 runs above average. There’s something wrong here although I wonder if it’s solely a velocity issue—perhaps movement is involved, as well—although that appears to be the most explicit explanation. Joba’s fastball has gone from a serious weapon to a significant burden and is now hurting him rather than helping him. When compared to previous years, in 2009, hitters are making contact with Joba’s pitches at a higher rate—80.4% compared to 73.5% in ’08—and this too, it seems, can be attributed to his weakened fastball. This is especially the case when he challenges someone outside of the zone (55.5% contact rate compared to 46.8% a year ago). He’s just more hittable than he has ever been in his short career. If his fastball is the issue, it doesn’t help that he throws the pitch more than anyone on the Yankees’ staff outside of A.J. Burnett.
However, maybe it’s not all the fastball’s fault. While I don’t know what to make of his velocity, maybe he could help his fastball out by improving his overall pitch selection. I think a lot of hitters choose not to swing at Joba’s slider—his second most used pitch—due to his command. He doesn’t really throw it much for strikes (that’s my subjective opinion). Further, he doesn’t throw his curveball much—only about 9% of the time—despite it being a good pitch. Therefore, hitters can simply wait out the fastball because they know it’s coming. This explains the higher contact rates. When the heat isn’t as good as it was in 2008, they hit it harder and more frequently. Joba would probably benefit from using the curve more often so as to offset a batter’s expectations. He’s essentially pitching with his bullpen repertoire (fastball, slider) and it’s hurting his fastball’s effectiveness. Perhaps that’s the main problem—predictable pitch selection—rather than the fastball itself (though the drop in fastball velocity is significant because of the predictability).
Or maybe the Yankees should just have Jose Molina catch all of Joba’s starts instead of Jorge Posada. I’m sure that would help (I’m kidding!).