Bang the Can Slowly: An Investigation into the 2017 Houston Astros

TL;DR

This paper statistically analyzes the 2017 Houston Astros sign-stealing scandal, providing evidence that their on-field performance was significantly influenced by the illicit sign-stealing tactics, affecting swing decisions, contact likelihood, and ball exit velocity.

Contribution

It offers a quantitative assessment of how sign-stealing impacted the Astros' batting performance during the 2017 season, which is a novel analysis of the scandal.

Findings

Astros' odds of swinging at pitches decreased by 27% when signs were stolen.

When Astros swung, contact probability increased by 80% on non-fastball pitches.

Ball exit velocity increased by approximately 2.39 mph when signs were known.

Abstract

This manuscript is a statistical investigation into the 2017 Major League Baseball scandal involving the Houston Astros, the World Series championship winner that same year. The Astros were alleged to have stolen their opponents' pitching signs in order to provide their batters with a potentially unfair advantage. This work finds compelling evidence that the Astros on-field performance was significantly affected by their sign-stealing ploy and quantifies the effects. The three main findings in the manuscript are: 1) the Astros' odds of swinging at a pitch were reduced by approximately 27% (OR: 0.725, 95% CI: (0.618, 0.850)) when the sign was stolen, 2) when an Astros player swung, the odds of making contact with the ball increased roughly 80% (OR: 1.805, 95% CI: (1.342, 2.675)) on non-fastball pitches, and 3) when the Astros made contact with a ball on a pitch in which the sign was known, the ball's exit velocity (launch speed) increased on average by 2.386 (95% CI: (0.334, 4.451)) miles per hour.