The Houston Astros’ sign‑stealing scheme is most closely associated with the 2017 MLB season, including the postseason, with some activity continuing into early 2018 before it was stopped.

Core timeline

  • The electronic sign‑stealing system was developed and outlined internally around September 2016 , when staff presented “Codebreaker,” a plan to decode opposing catchers’ signs using video.
  • The system was implemented during the 2017 regular season , using a center‑field camera feeding into a monitor near the dugout; players then banged on a trash can to signal upcoming off‑speed pitches.
  • MLB’s investigation later concluded the Astros illegally stole signs during the 2017 regular season and postseason , the year they won the World Series.

How long did it last?

  • MLB found that the main trash‑can based scheme continued into the 2018 regular season before players stopped using it, and there was no evidence of the same system in 2019.
  • There were also earlier, less formal efforts to use video for sign stealing discussed in 2016 , but 2017 is considered the peak and the season most fans mean when they ask “when did the Astros cheat.”

When it became public and punished

  • On November 12, 2019 , The Athletic published the whistleblower story (with ex‑Astro Mike Fiers on the record), which blew the scandal open and triggered MLB’s full investigation.
  • On January 13, 2020 , MLB announced its findings and punishments: one‑year suspensions for GM Jeff Luhnow and manager A.J. Hinch, a $5 million fine, and loss of first‑ and second‑round draft picks in 2020 and 2021; the Astros then fired Luhnow and Hinch the same day.

Quick “forum style” recap

In forum threads and fan debates, “when did the Astros cheat?” usually means:
they ran a camera‑based sign‑stealing operation mainly in 2017 , used some version into early 2018 , and got exposed and punished between late 2019 and early 2020.

TL;DR: The Astros’ cheating is tied primarily to the 2017 season (including playoffs) , with remnants into early 2018 , and it came to light in late 2019 with punishments in January 2020.

Information gathered from public forums or data available on the internet and portrayed here.