Within sports, membership in a fan base often constitutes an attachment to a team and its various personnel. As part of a presumed ingroup, sports fans will go about evaluating their favorite teams and players based on several factors, such as team or athlete performance and off‑the‑field behaviors by such athletes. Although a vast set of literature within sport management has reported that fans exhibit partiality towards their favorite teams, research in social psychology and group dynamics has presented evidence to dispute this occurrence. This body of work has contended that people in a group will operate using subjective group dynamics (SGD), wherein norms and values are actively considered in group appraisal. Complementary research has offered the manifestation of a black sheep effect (BSE), or ingroup extremity, particularly when members deviate from norms or standards of the group. In a similar vein, this dissertation challenges the prevalent notion of fans’ enduring support for their favorite teams and examines numerous correlates of such behavior. Through five main studies, this dissertation investigates the impact of athlete behavior, group membership, player status, rivalry, and regret on evaluative judgments, identity threat, purchase decisions, product choices, and social media behaviors. Study 1 gauged the role of ingroup extremity when a team’s expectations, or norms of performance by an athlete, are violated, providing evidence to support ingroup derogation among fans. Expanding upon these results, Study 2 offered an assessment of the BSE in determining how fans go about supporting and derogating an ingroup or outgroup athlete based on performance, while furthering the application of these concepts to purchase decisions and social media intentions. Our second experiment offers partial support of the BSE, wherein fans exhibit a proclivity to derogate deviant ingroup and outgroup athletes to the same extent. Using a multi‑method approach integrating both quantitative and qualitative methods, our third experiment tested how rivalry and membership (i.e., player) saliency operate to amplify specific aspects of fan behavior, social media intentions, and product choices. Study 3 reveals ingroup and performance biases among fans as well as the function of team identification as a guide for team-licensed merchandise selections. Study 4 examined how evaluations of deviant performance- and moral‑related behavior by athletes can be affected by various moral reasoning strategies utilized by fans. Our fourth experiment demonstrates similar biases as established in Study 3 and also illustrates the amplified use of moral rationalization over other moral reasoning strategies. Using the findings from our first four studies as a foundation, we introduce a novel concept to the field (i.e., black sheep regret [BSR]) and complete this dissertation with a field study (Study 5A) and an experimental investigation (Study 5B). Although Study 5A did not support BSR in a naturalistic context (i.e., on social media), Study 5B provides data to verify its occurrence in fans. Ultimately, Study 5B produces rationale for the inconclusive results within social media settings, explained by a potential effect of black sheep perpetuance (BSP). Taken together, this dissertation discusses its theoretical contributions and offers pragmatic implications and future directions for sport managers and practitioners within the sport industry. Ultimately, the current composition highlights the importance of multidisciplinary approaches in exploring various components of specific group behavior in fans, as well as in the larger milieu of human behavior itself.