On Sept. 22, 2016, an intern in the Houston Astros organization showed general manager Jeff Luhnow a PowerPoint presentation that featured the latest creation by the team’s high-tech front office: an Excel-based application programmed with an algorithm that could decode the opposing catchers’ signs. It was called “Codebreaker.”

This was the beginning of what has turned into one of the biggest scandals in Major League Baseball history. Throughout the 2017 season and for part of 2018, Astros baseball operations employees and...