Overview
Replay review uses video footage to verify disputed calls, introduced in NPB in 2010 for home run determinations (fair/foul, clearing the fence). The scope has expanded incrementally to include plays at the plate and outfield fence catches. The request system, allowing managers to challenge calls, was added in 2018 with two challenges per game (umpire-initiated reviews available from the ninth inning onward). While replay review has significantly improved call accuracy, the average two-to-three-minute review duration draws criticism for disrupting game flow. Ball-strike calls remain outside replay scope, and expansion into this area is debated. Tracking technology has reached the point where automated ball-strike judgments are technically feasible, but reconciling automation with baseball's tradition of human officiating remains an unresolved challenge.