[Editor’s note: This story has been updated to include a statement from the Red Sox and additional information from a source.]



When Major League Baseball punished the Red Sox and Yankees in September 2017 for conduct related to electronic sign stealing, the league touched on the epicenter of a problem that had been growing for years: The video replay room.



These rooms, intended to help managers decide whether to challenge umpires’ calls, were established after baseball introduced replay review in 2014. But some teams quickly realized the rooms also were easy places to learn a key piece of information: The sign sequence used by opposing pitchers and catchers.



Before the 2018 season, after years of barely enforcing its broad rules regarding replay rooms, the league made it crystal clear: Replay rooms cannot be used to help steal signs. The newly clarified rules, in combination with the fines the league levied on the Red Sox and Yankees and warnings...