Saturday, September 6, 2014

What's Wrong With Rafael Soriano?

Last night, Nationals closer Rafael Soriano blew a three-run lead, allowing two home runs to the Phillies (to add insult to injury, one was hit by Ben Revere). The outing before that, he blew another save. The outing before that, he got the save, but gave up a run in a rocky ninth inning.

Soriano's recent struggles have Nats fans screaming bloody murder about removing him from the closer's role. But they're failing to see Soriano for what he is: one of the game's best closers going through a rough patch of infinitesimal sample size.

What's wrong with Rafael Soriano? The short answer is nothing. The longer answer is random variance, factors out of his control, and the rest of this blog post.

In the first half, Soriano had a 0.97 ERA and a 0.811 WHIP. Since the All-Star break, he has had a 6.98 ERA and a 1.759 WHIP. These numbers measure results—which are important, to be sure. But pitching involves a lot of luck; it's been shown that pitchers have little to no control of what happens to a ball after it makes contact with a bat. So to measure the actual quality of Soriano's pitching, we need to fall back on what are known as his peripheral stats.

The main thing pitchers do have control over is throwing balls and strikes, and by extension walks and strikeouts. In the first half, when he was pitching lights-out, Soriano allowed 2.68 walks per nine innings and 8.76 strikeouts per nine innings—both quite good, if not elite, numbers. So far in the second half, Soriano has allowed 3.26 walks per nine innings and 8.84 strikeouts per nine innings. As a function of innings, then, his walks have increased slightly—which is not ideal, but 3.26 BB/9 is still above average—and his strikeouts have actually increased—which is obviously desirable.

Perhaps a better way to measure it is the percentage of batters Soriano has walked and struck out. In the first half, Soriano walked 8.2% of batters and struck out 26.7%. That's an average walk rate and an excellent strikeout rate. In the second half thus far, he's walked 7.5% of batters—an improvement—and struck out 20.4% of batters, which still rates as pretty good.

So Soriano isn't pitching significantly worse when it comes to balls and strikes. What has been worse (from Soriano's perspective) is hitters' contact with those pitches. In the first half, opposing batters had a .153 average, .222 on-base percentage, and .226 slugging percentage off Soriano and hit 0.24 home runs off him every nine innings. Since the All-Star break, opposing batters have hit .321/.387/.530 and 1.4 HR/9.

What accounts for this huge difference? As it turns out, mostly luck. We can use two stats to measure how unlucky a pitcher has been: BABIP (batting average on balls in play) and HR/FB (home runs allowed divided by fly balls allowed). These stats jump around a lot among players and among seasons for a given player, but with no discernible pattern: in other words, they are random variance, and they tend to normalize at a league-average rate over time. (This is because things like the quality and positioning of fielders is more important to deciding whether a ball drops in for a hit, and wind or the dimensions of a ballpark can turn a lazy fly ball into a home run—or vice versa—fairly easily.) Typically, batters "should" hit .300 on balls in play, and 9.5% of fly balls "should" be home runs. Truly talented pitchers can skew these numbers downward—particularly HR/FB—but not significantly.

Soriano's BABIP in the first half was .207 and his HR/FB was 2.2%. These numbers are almost impossibly good and suggest that Soriano was due for some regression; a player can't sustain a 0.97 ERA when it's built on unsustainable secondary stats like those.

But here in the second half, Soriano's BABIP has been .387, and his HR/FB has been 10.0%. Those numbers are also outliers, just like his first-half numbers—just in the opposite direction. A .387 BABIP is particularly unsustainable, and there is no way hitters can keep being this lucky off Soriano in the long term. Meanwhile, the HR/FB rate is also above the rate at which batters normally hit home runs—and it's also well above Soriano's career HR/FB rate of 7.7%. As we saw with the 1.4 HR/9, a big problem for Soriano in the second half has been the increased number of home runs off him, but if we dig deeper we can see that this is atypical for MLB hitters and downright aberrant for batsmen hitting off Soriano.

A final stat that can affect pitchers' luck is the rate at which they strand runners on base. League average LOB% (left-on-base percentage) is about 71% of runners stranded; it too can bounce around a lot for individual seasons for no apparent reason, but it always ends up around 71% in the long haul. In the first half, Soriano stranded 90.9% of runners, which is really lucky—many more of those runners should have crossed the plate. But in the second half, he has stranded just 62.9% of runners, which is fairly unlucky. A lot of those runners had no business scoring.

For Nats fans, it's certainly torture to see Soriano struggling like this—and doubtlessly it has been for Soriano too. But he can take solace in the knowledge that it's not really his fault—from the pitching side of things, he's continued to do things about as well as he's done for his entire career. When luck enters into the equation as much as it does with pitching, though, there are going to be stretches when even the best execution leads to crummy results. Small sample sizes (Soriano has pitched just 19.1 innings during the second half) can produce huge outliers; that's why baseball plays 162 games a season.

Although he has materially pitched the same throughout the year, the disparity between Soriano's extremely lucky results early on and his unlucky ones today is naturally going to catch the eye—and ire—of the fan base. Advanced stats show that, no, Soriano was never as good as he appeared to be in the first half—but he's also not nearly as bad a pitcher as he looks right now. The real Rafael Soriano is somewhere in between: a solid relief pitcher whose true value indeed lies around the average of his first and second half performances. Need proof? His ERA as it stands today (3.04) is almost a dead ringer for his FIP (3.16).

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