Arthur: The Astros’ Sign-Stealing left a fingerprint in the audio data

From SABR member Rob Arthur at Baseball Prospectus on November 15, 2019:

This week, we learned that the Astros used a crude system of monitors and audible signals to steal signs and communicated them to hitters at the plate. A camera in the outfield relayed a video feed to players in the tunnel, who whacked a trash can lid in order to relay what pitch was coming. In addition to being blatantly illegal–despite apologists’ counterarguments, the rules are very clear that no video technology can be used in real time–the Astros’ method left a plethora of evidence behind. The abundant traces of cheating allow us to go back and analyze when and how effectively they cheated.

The slamming sound of the trash can is so clear and distinct that it’s easily visible in the audio data. Here’s what a sample crash looks like in terms of volume.

(This particular audio sample comes from a September 2017 game which you can listen to here.)

Note the background noise level from immediately before and the two peaks, corresponding to two whacks on the lid, which was the signal for a breaking ball.

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Originally published: November 15, 2019. Last Updated: November 15, 2019.