As it stands right now, Chris Tillman is in the midst of his third minor league stint of the year while Jake Arrieta and Brad Bergesen toil in the Orioles rotation. None are pitching the way that the Orioles hoped, but while Tillman and Bergesen have become regular passengers on the Norfolk-Baltimore express, Arrieta has been allowed to make nine uninterrupted big league starts. Why is that? Has he really been better?
No, he hasn't. Arrieta has actually been worse at the big league level than both Bergesen and Tillman. A glance at his game log shows what appears to be about a 50/50 split between servicable starts and clunkers. It doesn't actually look half bad compared to Tillman's and Bergesen's game logs, and his 5.40 ERA, while ugly on its own, practically shines next to Tillman's 7.92 and Bergesen's 6.95. I suspect that it is because of these numbers that the current rotation talk is centered on Bergesen and if he should be sent down in favor of Tillman or perhaps even be replaced by someone like Mark Hendrickson. We haven't heard a peep from the Orioles about sending down Arrieta, despite the fact that if you look deeper, he has had more trouble at the big league level than have his two teammates.
Past and Future Performance
For the most part, Arrieta's success (relatively speaking) with the Orioles has been nothing more than smoke and mirrors. Both Tillman and Bergesen are pitching better than it appears on the surface, while Arrieta is pitching worse. His ERA is much lower than theirs, but when you look at the more accurate measure of FIP, all three pitchers are much closer together, with Tillman having been the best. Because FIP only focuses on what the pitcher can control, Arrieta can't hide from his horrendous walk and strikeout rates. He struggled with walks in the minors and it's only gotten worse since his promotion, as it currently sits at 5.21 BB/9. Just as bad is his K/9 of 3.91, which is about half what he put up in AAA. Bergesen's K/BB sits at 1.21, the only one of the three to have more strikeouts than walks. And that's even with his puny 3.72 K/9.
Thanks to FIP, we know that Bergesen has pitched slightly worse than Arrieta and Tillman slightly better, but xFIP is the best predictor of future performance, and it tells us that Arrieta stinks. In Tillman's six starts this season, he has an HR/FB ratio of 10.3%, which is just about where it should be. Arrieta, on the other hand, has been extremely lucky with an HR/FB of 8.5%, well below normal. Once that starts evening out, he'll be in for a shock. And poor Bergy is sporting an HR/FB of 12.7%. That high number has messed with his results, but the good news for him is that it has to go down eventually.
Batted Ball Data and Luck
Along with Arrieta's high walk rate and low strike out rate is another trend that doesn't match with his minor league numbers. In Norfolk this season, Arrieta had a ground ball rate of 49.5% and a fly ball rate of 29.9%, with similar numbers over his minor league career. He hasn't been able to repeat that so far in the majors. Of course there are plenty of fly ball pitchers who do well in the majors, but not while walking over five batters per nine innings. The ground ball has been one of Arrieta's strengths, especially since he has faced issues with his control. If he can't bring that back along with his strikeout totals, he'll never have success.
Bergesen's success in 2009 was built on a 50.1% ground ball rate, 2.34 BB/9, and quite a bit of luck. Despite his woes this year, his GB% and BB/9 have actually been good. His 47.2 GB% leads the Orioles starters and his 2.97 BB/9 is second only to Jeremy Guthrie. The difference between 2009 and 2010 is that Bergesen's HR/FB last year was very low at 8.3%, and his BABIP, at .289, was also below average.
So far this year it appears that the the fly balls Chris Tillman got last year have been turned into line drives. That's probably a function of all those fastballs he likes to leave over the plate, but given that he's only made six major league starts this season, it's hard to put too much stock in that. No regular starting pitcher this year or last year put up a LD% that high, and it stands to reason that it would come down some if he were allowed to keep pitching instead of being sent back to AAA every week.
So if Tillman and Bergesen have pitched better than Arrieta, why has Arrieta had better results? Luck, pretty much.
Poor Chris Tillman hasn't been able to catch a break on anything this season. His BABIP and LOB% are both ridiculous, making it no wonder his ERA is almost 8. If he ever gets the chance to pitch again in the majors (especially if they let him go more than two starts before sending him back down), maybe those numbers would begin to normalize. If we ever get a chance to find out is up to the Orioles.
Also getting jobbed, Brad Bergesen. A BABIP of .338, likely due to the fact that his infield defense is awful, a strand rate that is over 10% below normal, a high HR/FB, and constant talk of being sent down thanks to all three. Let's not confuse things: Bergesen isn't a great pitcher. Of the three, he's the least likely to have a successful major league career. But he is not this bad. And right now, he's not pitching as poorly as Arrieta.
Check out the BABIP on Arrieta. The normal BABIP range is .290-.300, so Arrieta is getting off easy when a batter puts the ball in play. There's no way he can keep that up over the season (especially with the defense behind him), and once that average goes up, it's going to combine with his walk rate for disaster. And if his HR/FB approaches the normal level? It'll be ugly.
If any pitcher gets sent down to AAA, it will probably be Brad Bergesen. But for my money, it's Jake Arrieta that needs more time in the minors. Between 2009-2010, Arrieta has made 28 AAA starts spanning 164.2 innings, but he still needs work. His walk rate was over 4 this year at AAA, something he needs to improve before he'll be ready for the majors. He also needs help with his secondary pitches, which have been simply awful since he made his debut. Only his fastball has a positive value at the major league level. His slider and curve ball have been below average, and his change up has been worse. Give him a chance to figure things out now, I say, so that he can be ready to contribute to the Orioles in 2011.
Stats courtesy of FanGraphs, Baseball Reference, and Minor League Splits.