This story originally appeared on Medium.
It’s a lot harder to get outs when batters don’t miss.
That’s probably the biggest problem that Clayton Kershaw faced that October night back in 2017. It was Game 5 of the World Series, and Kershaw’s Los Angeles Dodgers had split the previous games down the middle with the Houston Astros.
Kershaw, a three-time Cy Young award winner, had the chance to swing the series in his teams’ favor before returning to Los Angeles to play the remaining two games. He also had the chance to change his reputation: with a win, he would’ve gone from being seen as a brilliant regular-season performer who lacked what it took to get it done when it mattered most, to being remembered as one of the greatest all-around pitchers in the history of the game.
Instead, Kershaw surrendered six earned runs in just 4 ⅔ innings. The Dodgers lost Game 5, 13–12, and went on to lose the series. Kershaw threw his slider—infamous in its ability to make batters look foolish—39 times. He drew only one swing and miss.
There’s no asterisk next to Houston’s name in the record books quite yet—in fact, the Astros won’t even have to forfeit their 2017 title—but the sign-stealing scandal that rocked the baseball and sporting worlds still tarnishes the accomplishments of Houston’s title-winning team. The question remains: how much did the Astros benefit from the cheating strategies that they employed?
The first details of the complicated sign-stealing process were originally reported in November, but until recently, no data was formally available. It wasn’t until Tony Adams, a graphic designer and web developer, wrote a program that scraped data from all of Houston’s regular season home games. The result is a spreadsheet that documents, among other data, every pitch from every game, the type of pitch, the result of the pitch, and whether or not the pitch was preceded by a bang — indicative of a trash-can bang used to signal that an off-speed pitch was being thrown.
That any pitcher, let alone one of Clayton Kershaw’s calibre, would fail to draw more than one swing and miss on a slider is remarkable, but the advantage of throwing an off-speed pitch is ruined if the batter knows that one is coming. Though similar data from the World Series isn’t available, we can examine the regular season data over time (month by month) to see how Houston batters fared against off-speed pitches as the postseason approached.
The graph below charts the contact percentage, in raw numbers, of off-speed pitches that were preceded by bangs. Off-speed pitches include sliders, but also curveballs, changeups, and other pitches traditionally much slower than a fastball. The data omits pitches in which the batter did not swing, regardless of whether or not there was a bang before the pitch.
Though the percentages are not shown, Astros hitters generally made more contact on off-speed pitches as the season progressed. The numbers went from 66.67 percent in April, followed by 76.9, 79.7, 77.5, 79.5, and 81.1 percent in the subsequent months.
Analysis done by the Reddit user u/agilfix also helps make sense of the raw data. They showed that the Astros started using the bang method more often as the season progressed, and also became more accurate (i.e., a higher percentage of off-speed pitches followed the bangs). For instance, there were bangs on fewer than 50 pitches in the month of May, compared to over 400 in the month of August. The predictive accuracy of the bangs improved from 54.2 percent to 85.2 percent in those same months.
As shown in the above graph, Houston’s batters became more eager to swing at off-speed pitches preceded by bangs as the season progressed. The increase in accuracy on the method, in conjunction with presumptive confidence in the method, had direct results on the actions of the batters. The number of swings increased with the number of bangs, and the increase in contact percentage correlates to more balls put in play: more chances to score runs and win games.
The bang method may have been just one way of communicating signs to players—Major League Baseball commissioner Rob Manfred said that allegations that Astros players used buzzers lacked evidence, but couldn’t be ruled out—and it’s for now it’s impossible to know how often in Game 5 Houston knew that Kershaw was reaching back for his once-deadly slider. But it’s a lot harder to get outs when batters don’t miss — even harder when they know what’s coming.
