The 2017 Houston Astros used a center-field camera and trash can bangs to decode catcher signs in real time. Here is how baseball's coded signal system works, how the Astros broke it, and what MLB did about it.
In November 2019, former Houston Astros pitcher Mike Fiers told The Athletic that the Astros had stolen signs during their 2017 World Series championship season using a center-field camera and a system of trash can bangs relayed to batters in real time. The resulting MLB investigation, led by Commissioner Rob Manfred, confirmed the scheme and imposed penalties that included the suspension of general manager Jeff Luhnow and manager AJ Hinch, a $5 million fine, and the loss of first- and second-round draft picks in 2020 and 2021.
Baseball sign-stealing is as old as the sport itself. What made the Astros case different was the use of technology (a live video feed) to decode signs and the use of an audio signal (banging a trash can) to relay the decoded pitch type to the batter in real time. The scheme worked because baseball's sign system is a simple code, and like any simple code, it breaks under observation.
You can experiment with the same tap-based relay principle using the Tap Code tool, which encodes messages as paired taps on a surface.
The catcher-pitcher sign system is the foundation of baseball's coded communication. The catcher puts down fingers between their legs to tell the pitcher what pitch to throw. The system varies by team, but a common version works like this: one finger means fastball, two fingers mean curveball, three fingers mean slider, four fingers mean changeup. A second set of signs communicates location (inside, outside, low, high).
With a runner on second base, the catcher uses a more complex system with an indicator sign. The indicator tells the pitcher which of the subsequent signs is the real one. For example, if the indicator is a fist, the first finger count after the fist is the pitch. The catcher might put down: fist (indicator), two fingers (real sign: curveball), one finger (decoy), three fingers (decoy). A runner on second who does not know the indicator cannot tell which sign is real.
This is a keyed code. The indicator is the key. Without it, the signs are ambiguous. With it, the signs are unambiguous. The security depends on the runner on second not knowing the indicator, which changes from game to game or even inning to inning. The MLB rulebook governs what constitutes illegal sign-stealing, but the sign systems themselves are developed by individual teams.
Baseball's coded communication extends beyond the catcher-pitcher signs. The coaching staff uses a relay system to communicate with batters and baserunners. The third base coach gives signs to the batter (whether to bunt, take a pitch, or swing away) and to baserunners (whether to steal, hold, or execute a hit-and-run).
The third base coach's sign system uses a sequence of touches to body parts. A typical sequence: touch the hat (indicator), touch the left arm (real sign), touch the belt (decoy), touch the right arm (decoy). The indicator tells the receiver which subsequent touch is the real sign. This is the same keyed-code principle as the catcher's signs.
The dugout also relays signs to the third base coach, who relays them to the batter. This creates a chain: manager to dugout coach to third base coach to batter. Each link in the chain uses its own sign system. The complexity is deliberate. If an opposing team decodes one link, they still cannot decode the full chain without knowing all the indicators.
The Two Tap Code tool demonstrates a similar relay principle, where information is encoded in paired signals that require the receiver to know the pairing convention.
The Astros' scheme bypassed the entire security model of baseball signs by decoding the signs at the source. Here is how it worked, according to the MLB Commissioner's Report released in January 2020.
A camera in the center-field scoreboard at Minute Maid Park was focused on the catcher. The live video feed was routed to a monitor in the Astros' dugout tunnel. A staff member or player watched the monitor, decoded the catcher's signs in real time, and banged on a trash can to signal the pitch type to the batter. One bang meant fastball. Two bangs meant breaking ball. The batter heard the bangs and knew what pitch was coming.
This is a man-in-the-middle attack on the sign system. The catcher's signs were designed to be secure against a runner on second base, not against a camera with a live feed. The camera could see the signs clearly, and the live feed meant there was no delay. The trash can bangs were the relay channel, converting the decoded visual sign into an audio signal the batter could use.
The scheme was effective because it gave the batter approximately 2 to 3 seconds of advance knowledge of the pitch type. In a sport where a 95 mph fastball reaches home plate in about 0.4 seconds, knowing the pitch type in advance is a significant advantage. The Astros' slugging percentage at home during the 2017 season was anomalously high compared to their road performance, which is consistent with the sign-stealing scheme providing an advantage.
The scheme was discovered when former pitcher Mike Fiers spoke to The Athletic in November 2019. MLB's investigation found that the sign-stealing occurred during the 2017 season and continued into 2018, though the trash can banging was reportedly abandoned partway through 2018 after the team became aware that other organizations suspected the scheme.
Commissioner Rob Manfred released the investigation report on January 13, 2020. The report confirmed that the Astros used a center-field camera to steal signs during the 2017 regular season and postseason, including the World Series. The penalties were severe by MLB standards.
Jeff Luhnow (general manager) and AJ Hinch (manager) were suspended for one year each. Both were subsequently fired by the Astros. The organization was fined $5 million, the maximum allowed under MLB's constitution. The Astros lost their first- and second-round draft picks in both 2020 and 2021. No players were punished because Manfred determined that player immunity was necessary to obtain cooperation in the investigation.
The report also noted that the Boston Red Sox were under investigation for a separate sign-stealing scheme during the 2018 season. The Red Sox were later found to have used replay room equipment to decode signs and relay them to the dugout, though the scheme was deemed less systematic than the Astros'. The Red Sox were stripped of a second-round draft pick in 2020, and replay room coordinator J.T. Watkins was suspended for the 2020 season.
Manfred's report made a distinction between sign-stealing using observation from the field (which is legal and considered part of the game) and sign-stealing using electronic equipment (which is prohibited under MLB Rule 5.1.2). The rule states that clubs may not use electronic equipment to communicate information about pitches to the batter. The Astros violated this rule by using a live camera feed.
MLB implemented several changes after the 2020 investigation to prevent future electronic sign-stealing. The most significant was the introduction of PitchCom in 2022, a wireless communication device that allows the catcher to transmit pitch calls directly to the pitcher via an earpiece. The system eliminates the need for visible finger signs, making sign-stealing by camera impossible.
PitchCom uses encrypted radio transmission between the catcher's transmitter and the pitcher's receiver. The catcher presses buttons on a wrist-mounted pad to select pitch type and location. The pitcher hears the call in their earpiece. The system was optional in 2022 and became widely adopted. By 2023, most MLB teams used PitchCom as their primary sign communication method.
MLB also restricted the use of in-game video. Teams can no longer access live game feeds in the clubhouse or dugout during the game. Replay rooms are monitored by MLB personnel. The league installed cameras in clubhouses and dugouts to ensure compliance. These measures address the specific vulnerability the Astros exploited: live video access during the game.
For a different take on how tap-based signals work in sports, try the Tap Code Audio tool to hear how tap patterns encode letters, or read the companion post NFL Play-Calling Codes for another look at coded communication in professional sports.
The Astros used a center-field camera focused on the catcher, with a live video feed routed to a monitor in the dugout tunnel. A staff member decoded the catcher's finger signs in real time and banged on a trash can to relay the pitch type to the batter. One bang meant fastball, two bangs meant breaking ball. The scheme was confirmed by MLB's Commissioner's Report in January 2020.
Sign-stealing using observation from the field (such as a runner on second base reading the catcher's signs) is legal and considered part of the game. Sign-stealing using electronic equipment (cameras, live video feeds, replay room monitors) is prohibited under MLB Rule 5.1.2. The Astros violated this rule by using a live camera feed to decode signs.
General manager Jeff Luhnow and manager AJ Hinch were suspended for one year each (both were subsequently fired). The organization was fined $5 million. The Astros lost first- and second-round draft picks in 2020 and 2021. No players were punished because MLB granted immunity to obtain cooperation in the investigation.
PitchCom is a wireless communication device introduced by MLB in 2022. The catcher presses buttons on a wrist pad to select pitch type and location, and the pitcher hears the call through an earpiece. The system uses encrypted radio transmission and eliminates visible finger signs, making sign-stealing by camera impossible.
The catcher puts down fingers between their legs to signal the pitch type. One finger commonly means fastball, two mean curveball, three mean slider, four mean changeup. With a runner on second base, catchers use an indicator sign (such as a fist) that tells the pitcher which subsequent sign is real. The indicator is the key that makes the signs a keyed code rather than a simple substitution.
Tap Code
Prison communication system using taps on surfaces to encode letters in a 5x6 grid pattern.
Two-Tap Code
Encode and decode text using the Two-Tap (Knock Code) system where each letter is a count of taps.
Tap Code Audio Decoder
Decode tap code from live audio input using the Web Audio API. Detects knocks and taps through your microphone, maps them to the 5x5 Polybius grid, and outputs decoded text in real time. Includes a manual input fallback for typed tap sequences.
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