Risk taking is fundamental to organizational decision making. Extending prior work that has identified individual and situational antecedents of risk-taking, we explore a significant relational antecedent of risk-taking: rivalry. In both a field setting and a laboratory experiment, we describe how a competitor's identity and relationship with the decision maker influences risk-taking. We analyze play-by-play archival data from the National Football League and find that interactions with rival (versus non-rival) partners' increases risky behavior. In a laboratory experiment involving face-to-face competition, we demonstrate that rivalry increases risk-taking via two pathways: increased promotion focus and physiological arousal. These findings highlight the importance of incorporating relational characteristics to understand risk-taking. Our findings also advance our understanding of when and why competition promotes risk-taking, and underscore the importance of identity and relationships in the psychology and physiology of competitive decision making in organizations.