his article examines employee reactions to observing abusive supervision at work. Specifically, we integrate deonance theory with fairness theory and social cognitive theory to explore when and why employees who witness abuse toward a coworker engage in prosocial behavior intended to protect the victim. We first develop a moderated mediation model of prosocial responses to abuse, which identifies overall fairness as a first- and second-stage moderator, influencing the relationships between observed abusive supervision and observer deontic reactions and between deontic reactions and coworker protective behavior. Results from Study 1 support a model in which overall justice moderates the second link, indicating that fair norms and principles might prompt observers of abuse to direct their deontic anger toward coworker protective responses. Study 2 extends this work by further exploring the mediating mechanism by which overall fairness moderates the relationship between deontic anger and prosocial behavior for the coworker. Utilizing a critical incident technique, Study 2 reveals support for a mediated moderation model, indicating that the moderating effect of overall fairness occurs through its impact on ethical efficacy. These findings contribute to work on abusive supervision, third-party responses to injustice, and overall fairness by helping to better understand observer prosocial reactions to abusive supervision.