A disquieting combination of disproportionate importance and exceptional unpredictability

September 30, 2014

That title may sound a little like early stage investing, but it comes from a description of October baseball.  The Super-Rotation Rivalry explores the data behind the decision-making of two teams with very recent playoff history:  the Detroit Tigers and Oakland A’s.  (In both 2012 and 2013, Detroit eliminated the A’s because their ace – Justin Verlander – dominated in the final deciding game of the series.)

Both teams acquired aces at the trade deadline based on the theory that Moneyball may deliver results over a 162-game season, when the math has time to work, but in a short playoff series a team can be undone by a dominant pitcher or by cluster luck.

At the time it appeared as though those teams were likely to meet in the playoffs for a 3rd year in a row, so there was an element of game theory layered on top of the data analysis.  However the A’s swooned and landed in a single-elimination Wild Card playoff tonight in Kansas City.  Up 3 games on August 7, they went 18-30 to lose the division to the Angels by 10 games.

So we’ll have to wait to maybe see the game theory play out between the Tigers and A’s, but we will gather one more datum on the Moneyball-in-a-short-series argument.  (In this case, a very short series…)

Can stockpiling aces reduce playoff unpredictability?  It turns out the theory is hard to prove:

It’s possible there’s something to the “pitching wins pennants” hypothesis, but if so, it’s hard to see it in the stats. In 2012, Colin Wyers — then the director of research at Baseball Prospectus, now a “mathematical modeler” for the Astros — and I looked for evidence that teams with strong no. 1 starters outperformed expectations in the playoffs. We identified the ace of each playoff team from 1995 to 2011, rated each one using a normalized measure of ace-hood, and then checked for any correlation between the strength of each ace and the difference between his team’s regular-season and postseason winning percentages. There wasn’t one, which suggests that once you know a team’s regular-season record, knowing how good its best pitcher is doesn’t add any predictive power. Nor could Colin find any evidence of an effect after rerunning the analysis using the entirety of a team’s playoff rotation instead of its ace alone…

So why doesn’t the quality of a team’s top three starters or its ace register as significant? For one thing, the differences between teams are compressed in the playoffs, relative to the regular season: Teams with terrible staffs don’t make it to October, so the gulf between the best- and worst-pitching playoff teams isn’t as stark as we’re used to seeing during the season’s first six months. Perhaps more importantly, there’s more than one way to win baseball games, and even under an expanded playoff format, teams don’t get to October without doing something well. A team with an inferior pitching staff often makes up for its weakness on the mound by being better on offense.

If there’s no clear evidence that pitching acquires extra significance in the postseason, why is the belief that it does so persistent? It might be because it’s so hard not to notice the extent to which scoring is suppressed in the playoffs. There’s no question that playoff games tend to produce fewer crooked numbers: Last season, teams scored an average of 4.17 runs per game during the regular season, but in the postseason, their output declined to 3.78 runs per game, a 9.4 percent reduction. That figure fluctuates from year to year — in 2012, teams scored 19.2 percent fewer runs per game in the playoffs — but the direction of the difference is usually the same: down. During the 1995-2013 wild-card era, the gap has been exactly one run per game (half a run per team), or 10.6 percent.

Weather explains some of that effect; playoff games can be cold, and the lower the temperature, the less far the ball flies. Defense also plays a part, since playoff teams tend to be better than average at converting balls into outs. The bulk of the decline in scoring, however, stems from the difference in the postseason pitcher pool. … The pitchers on a given team’s postseason pitching staff are generally about half a run better than the same team’s full regular-season staff, and teams generally score about half a run less per game in the playoffs. The postseason scoring mystery is solved: It’s not that hitters lose their mojo once the calendar flips to October, it’s that they face superior opponents.

So in a sense, pitching is better during the playoffs, in that a team’s worst arms generally aren’t invited.

As it turns out, there are a few other hard-to-prove baseball theories that may be false:

Because October baseball subjects fans to a disquieting combination of disproportionate importance and exceptional unpredictability, it’s a fertile breeding ground for suspect narratives that attempt to explain small-sample postseason success or failure. Over the next few months, you might hear, for instance, that teams that “back into the playoffs” after a September slump are at a disadvantage against teams that end the regular season on a high note. Not so. You might be told that teams that rely on the home run can’t score in the playoffs, when small ball rules. In fact, the opposite is the case. Surely momentum matters? Uhuh. And we all know that there’s no substitute for postseason experience — except for a lack of postseason experience, which works just as well.


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