Sexual violence is a significant public health problem, particularly on college campuses, and disproportionately impacts women. Bystander intervention training has been identified as a promising intervention against sexual assault, as a third party is present in approximately one in three incidents of sexual assault. However, research has found that men report greater barriers to intervention and less efficacy and intention to intervene, thus require further attention. Theorists suggest that men’s masculine norm socialization may contribute to reluctance to intervene, but there is little understanding on the role that masculinity may play in facilitating intervention. The purpose of this study was to identify an outlier population of college men (N = 15) who have intervened against sexual assault, and to qualitatively examine the social and gender-relevant factors that influenced their intervention. Through a grounded theory analysis, the results indicated that the core category of “bystander intervention” was comprised of direct, indirect, and passive bystander behaviors. These behaviors were influenced by five key categories, which included: 1) exposure to training, 2) the role of alcohol, 3) social factors, 4) individual characteristics, and 5) masculine norms. These categories were salient for all participants, and differentially influenced and facilitated bystander intervention. Participants described their development and navigation of masculine norms, which in turn shaped their individual characteristics, exposure to training, and the ways in which they navigated the high-risk environments where they noticed potential assaults. Participants also described their decision-making process around intervening, and the strategies they used to intervene. These results offer a model for understanding college men’s bystander intervention against sexual assault, which incorporates both individual and social factors, as well as the complex role of masculine norms.