Stealing signs is believed to be particularly effective when there is a runner on second base who can both watch what hand signals the catcher is using to communicate with the pitcher and can easily relay to the batter any clues about what type of pitch may be coming.

In recent years, as cameras have proliferated in major league ballparks, teams have begun using the abundance of video to help them discern opponents’ signs, including the catcher’s signals to the pitcher.

As part of the inquiry, baseball investigators have interviewed the Red Sox team trainers and outfielder Chris Young, a former Yankees player.

In the clips, the Red Sox assistant athletic trainer, Jon Jochim, is seen looking at his Apple Watch and then passing information to outfielder Brock Holt and second baseman Dustin Pedroia, who was injured at the time but in uniform.

In baseball, the most infamous incident involving sign stealing played out in 1951, when the New York Giants overcame a 13 ½-game deficit over the final two months of the season to catch the Brooklyn Dodgers.