As of Wednesday night, Joba Chamberlain is back on the path to being a starting pitcher in the major leagues. And this Yankees fan couldn't be happier. For a team that was counting on Phil Hughes and Ian Kennedy to carry their rotation this season, and has been running Kei Igawa out there, the mere possibility of what Joba could bring is exciting.
But what's reasonable to expect from Joba as a starter? In The Book, Playing the Percentages in Baseball, MGL, Tango and Andy Dolphin found that in general, relievers have about a .8 run advantage in ERA over starters. Joba's season ERA of 2.66 would look more like 3.46. Surprisingly, the league ERA for the AL this year is only 4.05 at this point, so that only equates to a 117 ERA+. If we assume the league will end up with an ERA of around 4.40, then Joba would have an ERA+ of 127, putting him in the upper echelon of American League starters.
Of course we can't just assume a straight-line translation of his current stats (well, we could, but then this would be a really short post). First off, we're still dealing with a really small sample size. We can likely expect some regression to the mean going forward (somewhat technical note: the proper mean is likely not the average of all pitchers. If we have some reason to assume Joba fits into some other categorization, we'd want to regress to the mean for that category). Various projection systems have different ways of accounting for that expected regression. Let's look at what some of those systems had to say (all from before this season).
Dan Syzmborksi's ZIPS projected Joba to have a 4.43 ERA in 134 IP. Based on the innings pitched (although ZIPS doesn't predict playing time), I'm going to assume ZIPS either projected Joba solely as a starter, or perhaps in a hybrid role. Sean Smith's CHONE projections predicted Chamberlain to start 10 games, pitch only 65 innings (which works out to around 5 innings per start) and have an ERA of 3.88. Tango's Marcel projections only see Chamberlain throwing 37 innings at a 3.41 clip. Because of Joba's quick rise through the minors, the Marcel system doesn't have a lot to work with, which is reflected in the relatively low reliability Tango puts on that projection. I'd love to tell you what Baseball Prospectus and PECOTA predict, but I'm not a subscriber so we'll have to go without.
Since it appears that CHONE and Marcel assume Chamberlain is pitching in relief, let's add the same .8 runs to get a rough idea of Joba's projected performance as a starter. Assuming his current performance (plus the adjustment) as the best case projection, what is the range of possible performance based on projections?
Not much help there, since those range from substantially above average, to slightly below average. Although, at this point, I think the Yankees would be pretty happy if they could be assured of average performance for the rest of the season.
ERA is just one part of the equation, though (and we're not even quite done with that one yet). An even bigger question is how many innings will Joba be able to throw as a starter. He was a starter at Nebraska and the minors (although he averaged less than 6 innings per start in the minors), so he has demonstrated some ability to throws a starter's innings. According to PITCHf/x, there were roughly 97 pitches thrown per team in the first 6 innings of games during the 2005-2008 seasons. Let's use that number as a target for Joba.
In all of his major league appearances, Joba has never thrown more than the 38 pitches he used in the game 3 of the Division Series against Cleveland last year (the game after the midge game). He has four other appearances of over 30 pitches, including Wednesday night. For three of the four appearances of over 30 pitches that we have PITCHf/x data for, Joba doesn't appear to suffer at all from the number of pitches. There's no apparent difference between his fastball speed at the beginning and the end of those appearances. If anything, he's throwing a little harder at the end, which shouldn't be surprising. His long appearances tend to be the ones where he gets himself into a little bit of a jam. As we can guess from the mild controversy over Joba's enthusiastic reactions, adrenaline appears to play a big role in how he pitches, and a tight spot could easily lead him to throw harder. The one exception was the playoff game in Cleveland, where he throws 2-3 mph slower at the end of the appearance than at the beginning. I've got no compelling reason why we might see a dropoff there, except that it's the end of a long season.
In general, it seems appearances of 30+ pitches don't seem to really affect how Joba pitches. But 30 pitches is very different from 90 pitches. Joba's averaged right around 15 per inning, which would say he could get through 6 innings in 90 pitches. But that assumes he's able to not change his style.
The conventional wisdom is that pitchers throw harder as relievers than as starters because they don't have to pace themselves (one of the things that leads to the .8 difference in ERAs mentioned above). It's likely Joba's going to lose a few miles off all his pitches. The 98 mph fastball might drop to 93-94 on average while starting (just a guess, I'll have more research on that sometime next week), which probably makes it somewhat easier to hit. The big question, though, is what happens to Joba's slider. According to Josh Kalk, of the 184 pitches recorded, 66 of them were sliders - over 35%. Those sliders were essentially unhittable. Only 4 batters even managed to put one in play, and not a single batter got a hit over that sample.
But can Joba handle throwing the same percentage of sliders under a starter's workload? At that point, we're talking 30-40 sliders a game. I can only imagine the strain that would put on his arm (not being a pitcher or a doctor, I'm not really sure, but it sounds like a lot). And will those sliders be as effective if he takes a little bit off? Theoretically, Joba would start to mix in his curve and change a lot more, but those pitches aren't quite as polished as his slider, and certainly won't be as unhittable.
Obviously this is all conjecture, but what do I think is a reasonable expectation for Joba as a starter this season? Well, first, I think it's going to take a couple of months before he's "stretched out" enough to effectively start. I don't anticipate real starts (ones where he's expected to go 5+) until late July/early August. The timetable might be faster, if he's been building stamina by throwing on the side. As much as the Yankees have a plan to get him more innings at a time, they still need to win games - and Joba's usage pattern will be affected by that. If a starter is pitching really well in a tight game, will Giradi put Chamberlain in as planned?
But once Joba starts, I expect good things. Perhaps it would be more accurate to say I hope for good things. I do think the projections are all a little high. I'd go with an ERA of around 4.00 as a starter, averaging 5-6 innings per game. It's nothing spectacular, but it's a good start and would bode well for next season. I don't think Joba will be enough to get the Yankees to the playoffs this season by himself, but he should shore up the rotation and increase their chances.