BOSTON (CBS) — In November, MLB opened up an investigation into potential sign stealing by the Houston Astros. The investigation was broad, and it’s now ensnared the Boston Red Sox in controversy.

Ken Rosenthal and Evan Drellich of The Athletic reported Tuesday that during their historic 2018 regular season, the Red Sox illegally used their video replay room to try to steal opposing team’s sign sequences.

READ MORE: Julianne Nicholson, Medford Native, Wins Supporting Actress Emmy For 'Mare Of Easttown'

The replay room was designed so that teams could have staff members watch plays closely, to signal to the manager whether or not a play should be challenged. According to the report, some players would walk to that room “during games to learn the sign sequence opponents were using.”

The report was careful to note that this particular method of sign stealing was not particularly effective. And in the postseason, MLB essentially assigned a guard to the replay rooms, to ensure that no players could use the replay room for such shenanigans

“Red Sox sources said this system did not appear to be effective or even viable during the 2018 postseason, when the Red Sox went on to win the World Series,” the report said. “Opponents were leery enough of sign stealing — and knowledgeable enough about it — to constantly change their sign sequences. And, for the first time in the sport’s history, MLB instituted in-person monitors in the replay rooms, starting in the playoffs. For the entire regular season, those rooms had been left unguarded.”

Despite the limited effectiveness, a source “who was with the Red Sox in 2018″ did not downplay the actions.

“It’s cheating,” the person told The Athletic. “Because if you’re using a camera to zoom in on the crotch of the catcher, to break down the sign system, and then take that information and give it out to the runner, then he doesn’t have to steal it.”

MLB said they will launch an investigation into the 2018 Red Sox’ system in a statement released on Tuesday.

“The Commissioner made clear in a September 15, 2017 memorandum to clubs how seriously he would take any future violation of the regulations regarding use of electronic equipment or the inappropriate use of the video replay room,” the statement read. “Given these allegations, MLB will commence an investigation into this matter.”

For the uninitiated, the sign sequence is the way the pitcher receives a sign from the catcher, who (with a runner on base, and sometimes now with the bases empty) will put down multiple signs, with only one of those signs being active. In the simplest imaginable sequence, the pitcher could be reading the first signal thrown down by the catcher; the rest would just be dummy signs. In more elaborate sequences, the active sign could be the number of outs plus one, or the number of strikes in the count plus one. The active sign could also come after an indicator.

By watching video in the replay room and deciphering the sign sequence, a runner on second base would then be able to read the catcher’s sign and try to send a signal to the hitter at the plate to expect what pitch was coming.

READ MORE: CVS To Hire 1,100 New Employees In Massachusetts Ahead Of Winter

“Stealing signs was traditionally seen as a skill set,” UNH Sports Law Professor Michael McCann told WBZ. “The question is going to be whether or not baseball is going to do enough to stop it.”

It’s far from a simple system of “stealing signs,” but if true, using the replay room to attempt to decipher sign sequences would surely be a violation of the rules.

“It’s impossible to say for certain how much this system helped the Red Sox offense. But their lineup dominated in 2018, when they led the league in runs scored,” the report said.

The common link between the allegations against the Astros and the allegations against the Red Sox would be Boston manager Alex Cora, who was a bench coach with Houston prior to getting the job in Boston. Cora spoke with MLB investigators back in November. Cora told The Boston Globe at that time, “It would be irresponsible on my part to comment while it’s going on.”

The report from Rosenthal and Drellich gave the following assessment from people in baseball: “Many inside the sport believe there is cheating and then there is cheating-cheating. In this view, the Astros undertook the latter, while more indirect video-room efforts — at least before late 2017 — counted as the former.”

The report stated that teams were told that it was illegal to use the video replay room “to decode an opposing Club’s signs during the game,” but MLB did not assign monitors to the replay rooms until the 2018 postseason. The story also noted that hitters were allowed to visit the replay room in order to “study some video,” thus leading to an opportunity to look for more.

Famously, the Red Sox and Astros caused a stir during the ALCS that season, when an Astros employee was kicked out of an area at Fenway Park during Game 1.

The report noted that MLB has been lagging behind in terms of enforcing rules against teams using video to decipher signs: “As far back as 2015, the Yankees used the video replay room to learn other teams’ sign sequences, multiple sources told The Athletic. Other teams likely were doing the same. Sources said the Red Sox began doing it no later than 2016.”

An anonymous American League executive explained to the Athletic, “Oftentimes it takes a player to show up and be like ‘You f—– morons, you’re not doing this?’”

MORE NEWS: Sign Of Fall: Full Harvest Moon To Illuminate Night Sky

MLB has beefed up its enforcement of replay room monitoring, as the league tries its best to contend with developing technology impacting the game on the field.