Apr 25, 2013; Chicago, IL, USA; Chicago White Sox second baseman Jeff Keppinger (7) hits an RBI double against the Tampa Bay Rays during the first inning at U.S. Cellular Field. Mandatory Credit: Rob Grabowski-USA TODAY Sports

Rays Game 23 Preview: Jeff Keppinger and the Statistically-Improbable Breakout Year


Just a few months ago, Jeff Keppinger was a fan favorite at Tropicana Field, coming out of nowhere to become one of the Rays’ best hitters. On the season, he was incredible, managing a .325/.367/.439 line with 15 doubles, 9 homers, and 40 RBI in 418 plate appearances. He was so good that the Rays had virtually no chance of retaining him after the season, and sure enough he signed a 3-year, 12 million dollar contract with the Chicago White Sox. But his career in Chicago has seen entirely different results so far. IN 20 games, Keppinger has managed just .202/.198/.226 line with 2 doubles, 6 RBI, and 9 strikeouts without a walk in 86 plate appearances. It’s unbelievable that a player who looked better than ever has recently as last season has suddenly come apart.

Keppinger has gotten off to a horrific start, but the good news is that he’s beginning to break out of it. In his last 3 games, he has gone 2 for 4 each time, raising his batting average from .153 to .202. But there’s still plenty of reason for concern. Kepppinger is showing no plate discipline at all, with his batting average higher than his on-base percentage as he hasn’t walked or gotten hit by a pitch but has 2 sac flies. You have to think that this won’t persist, but as it stands right now, Keppinger is the 21st player, the first since Midre Cummings in 1996, to have a greater batting average than OBP after 85 plate appearances. He’s just the sixth non-pitcher. And that lack of selectivity hasn’t just affected Keppinger’s ability to hit the ball with any authority as his isolated power is just .024. He’s actually hitting a lot of line drives, 29% of his batted balls compared to the 21% league average, but his BAbip (batting average on balls in play) on those line drives is just .591, well below the league average of .679. He’s not getting any hits on groundballs either, managing just a .133 BAbip compared to the .223 average, and he doesn’t have a single hit on a flyball all year, obviously below the .103 league BAbip. On the whole, Keppinger’s BAbip is just .221, well below the .292 league average. Maybe he’s coming around now, but didn’t it seem like at the beginning of the year, Keppinger had just completely fallen apart? Don’t all those difference in BAbip seem so significant? In fact, they’re not.

The probability of Keppinger managing a BAbip as low he did on line drives was actually .188, a little less likely than 1 in 5, something that’s well within the range of normal. For groundballs, the probability was .098, less likely but also not a significant value. On flyballs, we have our first significant p-value (probability value) at .045, and that’s something that we can attempt to explain because when non-power hitters hit too many flyballs, the results are not good, even if they’re certainly due for more than the zero hits Keppinger has gotten. And overall on the year, Keppinger’s BAbip of .221 isn’t significantly lower than the league average, coming in at a p-value of .085. What does all of this tell us? On the whole, Jeff Keppinger has really just been a victim of terribly bad luck, and that’s what has torn apart the rest of his game.

In the face of Keppinger’s improbable breakout in 2012, his struggles to begin 2013 are very funny from a statistical perspective. It can be viewed as a regression to the mean, an extreme value above what we would expect being canceled out by an extreme value going the other way. But regression to the mean isn’t quite that magical and that convenient, and the big statistical point here is something different. There’s a concept in statistics that if you run enough statistical tests, some are going to be significant by chance alone. If you think of every player in baseball as a statistical test, it’s clear that some of them are going to have breakout years or disastrous ones simply because of luck. When a player does have one of those years, it’s up to teams to figure out whether it was because of a real breakthrough or decline or just a case of fortune playing games with us. And if you want to assess whether a player has really broken through, sometimes the stats don’t tell the entire story–watch him play and see if anything really has changed.

The case of Keppinger demonstrates just how crazy luck can be and that we should remain levelheaded both when players are doing surprisingly well or suspiciously not. Sometimes, for reasons out of our control, a player like Keppinger can have a shocking breakout year, and we just have to realize that the supposed breakthrough may not be real. Rays fans wish Keppinger nothing but the best for Keppinger over the next three years (except, of course, when he plays the Rays). But even while we basked in the glory of his 2012 season with the Rays, we can acknowledge that he was not nearly as good as he played and that maybe he just got lucky. We can also be confident, though, that Keppinger is substantially better than he has played in the early goings of 2013 and that his numbers by the end of this year will indicate that. Even if he won’t be a star for the White Sox like he was during his brief time with the Rays, Keppinger can at least be a solid player like he has been most of his career. A great season last year and a tough start to this year doesn’t change that one bit.

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  • Baltar

    Great statistical analysis, Robbie. I love it when you do stuff like this.

    My own amateur opinion of Kepp after his great season last year was that it was a fluke, and so far that appears to be the case, but that’s far from certain.

    The White Sox signing of him was a reasonable small gamble. At $12M for 3 years, he will be a bargain even if he accumulates as little as 3 WAR. At worst, it’s a small dent in their $120M budget.