I think it will be helpful to look at three different seasons for Joba. First, 2009, the only year he was used as a starter in exclusivity (he did have 1 relief appearance, but 31 starts). Then,.2010, when he first moved to the bullpen full time, and because of injuries, really the only year he has been in the bullpen for a full year. As a starter, he was okay, below average, but a quality back of the rotation piece. In 2010, he had a very mediocre year in the bullpen by ERA, but had a good year by defensive independent metrics. The third year in this post that I'll look at is so far in 2013, as we want to determine whether or not he still has present value, by comparing this year to the two previous years, where he did have value.
I'll also break it down by platoon splits, as for his career, Joba has been about equally effective against both lefties and righties, and he was in 2009 and 2010 as well. Obviously 2013 is too small of a sample size to look at splits, but breaking up the graphs by splits gives us a better idea of how he is actually pitching on the whole. First, let's look at how he has pitched lefties since 2008 (including the years we aren't looking at individually)
n platoon splits. He makes sure he throws it lower to lefties on average, as you can see by looking at how he is pitched right-handed batters for his career
The fastball is located both high and low about equally in 2010, showing how he was pitching lower that season. The curve was kept either further away from lefties that season as well. Fast forward to how he is pitching lefties so far this year:
Joba is getting the whiffs in slider and curveball locations and they are on pitches that he is taking velocity off of on average. The home runs are coming when he isn't getting the ball glove side, and his contact allowed is coming on pitches that are a little higher and more glove side than his average pitch. Compared to 2009-2010, his whiffs are coming on much lower pitches on average this year, but his home runs allowed are lower, and his contact is about the same:
Maybe there is a sequencing problem or maybe he is doing some kind of pitch tipping or has a release point that is easy to see. Because of the current numbers, and the injury concerns, Joba doesn't have much real value when it comes to the trade market, but I think he could be an interesting buy low guy. His command doesn't look broken, at least by average locations (he can still locate both arm side and glove side depending on platoon), and his stuff is still really good. Preferably, he gets the fastball up higher on average, but he has the tools to succeed, especially if he gets away from Yankee Stadium where he has struggled.