Knowing which pitch will be coming gives batters a huge
advantage. It is why trying to steal a catcher’s signs to the pitcher is
almost as old as the game of baseball. It is usually not contrary to the
rules and is actually considered a bit of gamesmanship.
However, what got Boston in trouble was their use of Apple Watches in
the dugout in their attempt at stealing the Yankees’ signs. Here is the
approach that Boston is believed to have used.
The catcher uses his fingers to signal a number to the pitcher conveying
what pitch he wants thrown. However, when a runner is on second base
(that can see the catcher’s signal and perhaps even tip off the batter),
the real sign is disguised by the catcher in a series of numbers.
Boston studied video replay during the game to examine the signs used by
the Yankees catcher when there was a runner on second base. Boston also
recorded the types of pitches that were being thrown. By matching up the
signals of the catcher with the type of pitches thrown, they were able
to determine how to decode the signs.