Advancements in technology have allowed for robot umpires in baseball, replacing human umpires to minimize errors in judgment: strike/ ball decision. Yet, when watching games with robot umpires in pilot operations, there are some instances where the robot umpire also commits erroneous calls. Hence, this study would conduct a scenario-based online experiment to investigate how spectators perceive robot umpires in baseball games depending on the subject of error (robot umpire vs. human umpire). The experimental results would indicate that people demonstrate a lower degree of trust, attitude, and call credibility on robot umpires. Furthermore, the effects of robot umpires would be moderated by the familiarity of the robot umpire and by the phase of error (early vs. late in the game). These findings would contribute to the understanding of the spectator’s perception of new technologies replacing humans and have practical implications for sports industry practitioners.