Arthur: Astros’ offense took a huge leap after they started stealing signs

From SABR member Rob Arthur at Baseball Prospectus on November 22, 2019:

At this point, it’s definitive: in 2017, the Houston Astros used an elaborate system of real-time video and trash can banging to steal and relay signs to hitters at the plate, cueing them in to whether a non-fastball was coming. From the original reporting done by Ken Rosenthal and Evan Drellich to leaked emails to an endless queue of videos showing the system in action to an audio analysis I did last week to literal photographs of the monitor, a mountain of evidence is accumulating that the scheme existed and was against the rules.

But despite the certainty that the Astros were stealing signs, there’s been frustratingly little confirmation that it actually helped them at the plate. Ostensibly, the scheme was limited to home games, but the Astros somehow performed better on the road. Likewise, there’s little signal that they improved more than expected from 2016 to 2017. Rather than slicing the data either of those two ways, I looked for when in 2017 the Astros first began cracking catcher codes. It turns out that the Astros offense jump-started at around the same time, suggesting that the sign-stealing scheme was extremely effective.

From the earliest reporting by Rosenthal and Drellich, it was clear that the system wasn’t in operation at the very beginning of the 2017 season. They mention a “a hitter who was struggling at the plate” (likely Carlos Beltran) as one of the architects, implying that he had already racked up some plate appearances. Other people—such as ESPN writer Sam Miller—who have examined the Astros video archives didn’t hear the characteristic sound of the trash can until the end of May. So there was good reason to believe that the Astros didn’t have their system up and running from the beginning of the year. That leaves us a narrow window of time to examine the Astros performance before and after they started intercepting signals.

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Originally published: November 25, 2019. Last Updated: November 25, 2019.