This mixed-methods study examined the association between high school sport coaches’ moral disengagement and their perceived coaching efficacy, and began to explore coaches’ justifications of and consequences for the hostile aggression exhibited by their athletes. High school coaches in the United States ( N = 449) completed online surveys that included the Moral Disengagement in Sport Scale, Coaching Efficacy Scale II-High School Teams, and questions regarding their beliefs about and responses to athlete’s hostile aggressive behaviors. Hierarchical regression analyses were conducted to determine the association between coaches’ moral disengagement and their perceived coaching efficacy, and multiple analysis of variance explored differences in moral disengagement and coaching efficacy based on coaches’ justifications for athletes’ hostile aggression. Qualitative analyses involved coding coaches’ responses to questions of when they believed hostile aggression displayed by athletes was justified, and their typical responses to athletes’ hostile aggression. Results suggested that coaches’ moral disengagement was a negative predictor of their total perceived coaching efficacy, as well as specific aspects of their perceived coaching efficacy. Further, a majority of coaches indicated that hostile aggression was never acceptable or justified. Based on these results, differences in moral disengagement were found between coaches who did and did not justify athlete hostile aggression. The most common consequences for hostile aggression involved reduced playing time and additional physical conditioning. The current findings highlight the significance of coaches’ moral disengagement as it relates to their coaching, supporting a need for greater coaching education around coaching philosophies and approaches to disciplining athletes.