Trevor Plouffe, a nine-year veteran who last played in 2018, explained that the Astros used a live feed to capture the opposing catcher's signals to the pitcher, then used technology to relay that information to the bullpen catcher, who would then indicate whether the pitch was a fastball or offspeed by putting his hands up on the fence or keeping them down. Plouffe's information came courtesy of big-league pitcher Carson Smith as well as an unnamed source.
On Thursday, Major League Baseball broadened the investigation - which originated as a probe into the 2017 Astros squad - to include Houston's 2019 club, as well as other teams.
Plouffe is the latest player to speak out regarding the sign-stealing controversy. Active right-handed pitcher Mike Fiers previously said that the 2017 team, which he was a part of, illegally used surveillance.
MLB has not yet made a ruling and no penalties have been filed against the Astros.
Plouffe spent seven years as a member of the Minnesota Twins and made brief appearances with the Oakland Athletics, Tampa Bay Rays, and Philadelphia Phillies.