The National Collegiate Athletic Association (NCAA) established policies for the inclusion of transgender athletes to compete in collegiate sport that align with their gender identity. Despite this access, the extent to which collegiate sport environments are welcoming, inclusive and supportive of transgender athletes is unclear. Understanding coaches' perceptions and attitudes is particularly salient given the critical, and often personal, nature of coach-athlete relationships and the impact coaches have on sport environments [Kuhlin, F., Barker-Ruchti, N., & Stewart, C. (2020). Long-term impact of the coach-athlete relationship on development, health and wellbeing: stories from a figure skater. "Sports Coaching Review," 9(2), 208-230; Stirling, A. E., & Kerr, G. A. (2013). The perceived effects of elite athletes' experiences of emotional abuse in the coach-athlete relationship. "International Journal of Sport and Exercise Psychology," 11(1), 87-100]. NCAA coaches' perceptions of, and attitudes towards the inclusion of transgender athletes is unknown, and thus the degree to which coaches are creating safe, or harmful, environments for transgender athletes is unknown. The present study aims investigate coaches' perceptions to be able to inform policy and education for promoting inclusive, safe environments for transgender athletes. We asked NCAA coaches (N = 1358) to describe the reasoning for their beliefs regarding the inclusion of transgender athletes in collegiate sports. Through reflexive thematic analysis, we determined coaches' reasoning for their perceptions, within the context of five higher-order themes: (a) It's not right: Transgender identities as invalid, (b) A need to protect (cis) women's sports, (c) Transgender rights are human rights, (d) Sport's role in society and coaches' role in sport and (e) I am not sure what I believe. Analyses illuminate avenues for transgender athlete inclusion training for coaches.