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Oakland A's by the numbers: The best rotation in the American League

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Jesse Chavez just keeps getting better and better.
Jesse Chavez just keeps getting better and better.
Ezra Shaw/Getty Images

The Oakland A's have won nine of their last 12 games, and a big reason for that resurgence has been their pitching. The hurlers have allowed just 26 total runs in those 12 contests, including three shutouts and two more instances of only one run. The bullpen has stabilized a bit, too -- it hasn't blown a save since May 15, nor recorded a loss since May 16. But the rotation has been the real story.

Oakland's rotation leads the American League in starter's ERA, and it's not particularly close:

1. Athletics: 3.10
2. Rays: 3.33
3. Angels: 3.71
4. Mariners: 3.82
5. Twins: 3.96

They're nearly a full run better than the fifth-place team, and they are a full run better than the league average (4.12). They've also held opponents to the lowest OPS (.614) and fewest home runs (22) of any team's starters. During the current 9-3 stretch over the last 12 games, the rotation has posted the following line:

A's rotation: 12 starts, 1.36 ERA, 79⅔ innings, 55 Ks, 17 BB, 56 hits, 3 HR

If you remove the starts in which Kazmir and Sonny left with injury scares, the per-start average jumps from 6⅔ innings to just over 7 frames. Even crazier, half of those 12 games have been started by Kendall Graveman and Jesse Hahn, the two young guys and relatively weak links in the group, so this hasn't even been just Sonny carrying everybody on his shoulders. The whole group is on fire. Here's a key stat for each starter.

Sonny Gray | 1.65

That's his ERA, the best in all of baseball. Of course, no ERA that low is truly sustainable, so how for-real and how fluky has Sonny's dominance been so far? We'll start with a few easy numbers. He ranks third in MLB in innings and seventh in FIP (2.65), so he's going as deep into games as anyone and he's not just relying on batted ball luck. His strikeout rate is strong, and his walks are down substantially from last year; as a result, his K/BB rate has gone from 2.47 last year to 3.48 this season. Good start!

If you're looking for something to complain about, one part of his performance may be tough to repeat -- opponents have utterly failed to record hits or homers against him. The following numbers are his opponent's batting average (BAA), his home runs per 9 innings (HR/9), and the percentage of his fly balls that clear the fence for homers (HR/FB).

Sonny, 2015: .186 BAA, 0.33 HR/9, 4.3% HR/FB
Sonny, 2013-14: .228 BAA, 0.60 HR/9, 9.2% HR/FB

Sonny has always been good at limiting home runs, dating back to the minors and probably college and most likely Little League, so it's not surprising to see him do so again. He keeps the ball on the ground 55% of the time, and you can't homer on a ground ball. He also strikes out nearly a quarter of the batters he faces, and you can't homer on a strikeout. His career HR/FB rate is actually right around average, but since he allows so few fly balls overall there aren't many chances for homers. However, he's gone a step further this year, cutting that HR/FB rate in half, and I think that enters the realm of small-sample fluke; expect a couple more flies to find seats the rest of the way, but only a couple.

As for the batting average, the smart money is that it'll come up but there are no guarantees. I hate to fall back on a cliche stat, but Sonny's BABIP has dropped 40 points and I don't see a good reason why that should continue for a groundball pitcher. Sonny's low career BAA makes sense and falls in line with other high-grounder, high-strikeout guys like Felix, Gerrit Cole, and Francisco Liriano, but there's no way to reasonably expect that .186 mark to continue all year. He's also leaving a lot more runners on base (increased LOB%), and while that could be a function of an increasing ability to get out of jams, it's more likely a small-sample success that won't continue.

All we can say for now is that Sonny is incredible, and he's leading the world in ERA. That ERA will probably come up a bit as he gives up a couple more hits and a couple more homers and succumbs to just a couple extra rallies. But it won't necessarily come up that much, maybe not even a full run. Sonny has emerged as one of the elite pitchers in the sport, and on top of that he's playing out of his mind right now.

Jesse Chavez | 6⅔

That's the number of innings he's averaging in his eight starts, which is second-best on the team after Sonny. He's also struck out three batters per walk and posted a 2.38 ERA in those starts, and somehow he's keeping the ball in the park too. That last part might not continue and that will cause a few extra runs to score, but Chavez is making it more and more clear that last year was a building block rather than beginner's luck. His velocity is up a tick this year, especially on his cutter, and both Brooks and Fangraphs agree that his curveball is slowly being replaced by a slider -- I'm not concluding anything from those facts, just mentioning them, both for your general knowledge and to show that he's still developing his game as a starter.

His overall season ERA of 2.11 is fourth in the entire AL, behind only Sonny, Dallas Keuchel, and Chris Archer. Granted, fifth place is held by Mike Pelfrey, just to prove that flukes can still exist in early June, but Sonny/Chavez is shaping up to be the kind of elite 1-2 punch that Billy Beane so desperately wanted in his rotation last summer.

Jesse Hahn | 7.25

That's his strikeouts-per-nine-innings if you drop his first three starts and just look at his last eight outings. That kind of solid strikeout rate, combined with a groundball rate of 52%, will get you through a lot of scoreless innings -- it's exactly what we just discussed with Sonny, who is at 8.0 K/9 and 55% grounders. Here's the difference from his first three starts:

Hahn, starts 1-3: 17 innings, 5 Ks, 2.65 K/9, 7.5% of batters
Hahn. starts 4-11: 49⅔ innings, 40 Ks, 7.25 K/9, 19% of batters

Strikeouts aren't the only way to succeed as a pitcher, but they sure don't hurt. His improved rate is still somewhat lower than what he did last year for the Padres, but then, he's facing DH's instead of pitchers now that he's in the AL. A K/9 in the neighborhood of "7ish" is about what his minor league career would reasonably suggest, so I don't think it's unfair to say that the Hahn we're seeing is closer to the real thing than the Hahn we saw struggling to find himself in April. (By the way: For the season, his 45 strikeouts have come with only 14 walks, for a K/BB rate of 3.21. Not bad for a 25-year old!)

Kendall Graveman | 1.50

That's his rate of ground balls to fly balls in his three starts since rejoining the rotation, made up of 36 grounders and 24 flies. In his first four starts, he induced just 27 grounders but allowed 37 balls in the air, for a rate of 0.73 grounders per fly. This particular stat is paramount to Graveman's success, because his entire game plan is based on getting hitters to pound the ball into the ground for easy, efficient outs. Whereas Hahn is able to miss enough bats to add some strikeouts to his grounders, Graveman can't do that as reliably and therefore has to focus on getting that weak contact using his sinker -- and if it starts coming in the form of flies and liners then he's going to get knocked around like he did in April. He looked lost in that first MLB trial, but we're seeing a completely different pitcher now. He's throwing strikes, he's getting ahead of hitters, and he's keeping the ball on the ground. That's how Graveman was advertised when Oakland acquired him, and it's a strategy that will lead him to a lot of 10-pitch, 1-2-3 innings (though also an occasional five-hit, three-run rally).

Graveman, last 3 starts: 17⅔ innings, 3.06 ERA, 11 Ks, 6 BB, 18 hits, 1 HR, 1.50 GB/FB

Scott Kazmir | 8

That's the numbers days he's had to rest since his last outing. On May 27, Kazmir left after three innings with shoulder tightness, but his MRI came back clean and he only skipped one start. All systems are go and he's slated to pitch today (Friday) against the Red Sox. You always have to hold your breath a bit with Kazmir, considering that the main reason the A's were able to afford him in the first place was his extensive history of injury and inconsistent effectiveness. However, I'm reminded of last April, when he left a start due to triceps tightness and then came back to throw eight innings in his next outing. Not every bit of creakiness is a death warrant, and it's worth noting that this is the first time he's missed a start since signing with Oakland -- if the problem lingers, Drew Pomeranz is already here, ready to fill in. We'll learn today if that shoulder issue was just a bump in the road or something to be concerned about. And hey, his 2.93 ERA is still good for 11th in the AL!

***

I want to conclude with a rough analogy. When Graveman began the year, he got torched. Now, he's gotten himself to the point where he's putting up a lot of zeroes, but then getting done in by one big inning in which he can't hold it together. That was the point that Hahn was at to start the season, but now Hahn has ironed things out a bit and his one bad inning is only yielding 1-2 runs instead of his entire lead. That's sort of the point that Sonny was at last year, able to get through a seven-inning game with only one rough inning that didn't usually cost him anything. But now, Sonny has taken the next step too, and he's dominating throughout entire outings; when he gives up a run, all it seems to do is spoil his shutout bid instead of mattering in the context of the game. It's an interesting look at the evolution of young starting pitchers, unfolding right before our eyes.