Overview
Sign stealing refers to the illicit decoding of a catcher's pitch signals or bench-relayed strategic signs by the opposing team, which are then communicated to the batter or baserunners. Signs form the tactical backbone of baseball, and compromising their secrecy undermines the fundamental fairness of the game. Sign stealing falls into two broad categories. The first is runner-based sign stealing, where a runner on second base visually reads the catcher's signs and relays them to the batter through gestures - a gray-area practice that has existed for as long as the game itself. The second is electronic sign stealing, which uses in-stadium cameras, monitors, or other devices to systematically decode signs; this is explicitly banned by both MLB and NPB. The 2017 Houston Astros scandal epitomized the latter: the club used a center-field camera to capture catcher signs and relayed pitch types to batters by banging on a trash can in the dugout, resulting in the permanent suspension of the manager and general manager. NPB has also faced sign-stealing allegations over the years, prompting successive rule tightening. In recent seasons, encrypted electronic communication devices between pitcher and catcher have been approved, representing a technological countermeasure against sign theft.