Adolescent relationship abuse (ARA) is a significant public health problem. Coaching Boys Into Men (CBIM) is an evidence-based ARA prevention program that trains coaches to deliver violence prevention messages to male athletes. Assessing acceptability and impact of CBIM on coaches may inform prevention efforts that involve these important adults in health promotion among youth. As part of a two-armed cluster-randomized controlled trial of CBIM in 16 high schools in Northern California, coaches completed baseline and postseason surveys (n = 176) to assess their attitudes and confidence delivering the program. Coaches in the intervention arm also participated in interviews (n = 36) that explored program acceptability, feasibility, and impact. Relative to controls, intervention coaches showed increases in confidence intervening when witnessing abusive behaviors among their athletes, greater bystander intervention, and greater frequency of violence-related discussions with athletes and other coaches. Coaches reported the program was easy to implement and valuable for their athletes. Findings illustrate the value of exploring attitudinal and behavioral changes among ARA prevention implementers, and suggest that coaches can gain confidence and enact behaviors to discourage ARA among male athletes. Coaches found the program to be feasible and valuable, which suggests potential for long-term uptake and sustainability.