Barry Svrluga of the Washington Post broke down what Nationals pitchers and catchers did during the Fall Classic:
"First, each pitcher had to have his own set of signs, and catchers Yan Gomes and Kurt Suzuki had to be familiar with each one. So the staff printed out cards with the codes and had them laminated. The catchers could have them in their wristbands, a la an NFL quarterback with play calls strapped to his forearm, and the pitchers would have them in their caps. Each pitcher had five sets of signs, and they could change them from game to game—or even batter to batter, if necessary. Using the set labeled No. 2, but worried the Astros were catching on? The pitcher could signal to the catcher to move to set No. 3. ...
"Next came the way the Nats employed their signs, which was nontraditional. Rather than just use, say, the second sign the catcher put down, the Nats might 'chase the two.' That meant the pitcher would watch for the catcher to put two fingers down, and then throw the pitch that corresponded to the following sign. Or they could play 'outs plus one.' So if there was one out, the pitch would be the second sign the catcher put down. If there were no outs, it would be the first sign. 'Strikes plus one' worked the same way."
Nationals pitching coach Paul Menhart told Svrluga the plan was their "best way to counteract anything that might have been going on."
"It was mainly because we thought we had heard some whistling," Menhart said. "Did we really hear it? Whether you do or you don't, just to put those thoughts in our minds is dangerous. So we just said, 'Let's nip this now.'"
While stealing signs has been a part of Major League Baseball for decades, the Astros reportedly took the tactic to new heights in their attempts to gain an advantage over the opposition.
Former Astros pitcher Mike Fiers, who plays for the Oakland Athletics, told The Athletic's Ken Rosenthal and Evan Drellich the organization established a sign-stealing system in 2017 using a camera positioned in the outfield and the help of "at least some on the baseball operations staff."
Per Rosenthal and Drellich, Astros players and employees would carefully watch the camera feed to see the opposing catcher's signs and would then alert their hitter to what pitch was coming by banging on a trash can, which would typically indicate an offspeed pitch was coming.
"Regarding the story posted by The Athletic earlier today, the Houston Astros organization has begun an investigation in cooperation with Major League Baseball," the organization said in a statement, via MLB.com's Brian McTaggart. "It would not be appropriate to comment further on this matter at this time."
ESPN's Jeff Passan reported Thursday that MLB's investigation into illegal sign-stealing is expected to be expansive and will include more teams beyond the 2017 Astros, with potential penalties being "unlike anything seen in the sport's recent history" if any wrongdoing can be proved.
Members of the Astros and Boston Red Sox have already been contacted by the league, per Passan.
Houston won the World Series in 2017 by beating the Los Angeles Dodgers in seven games. The team reached the Fall Classic again this season but lost to Washington in seven games.
The Nationals pitching staff held the Astros to 30 runs in the series, including 11 in four games at Minute Maid Park.