Adolescent sport participants, particularly girls, continue to drop out of sport at alarmingly high rates, which presents an opportunity for new sport programs to enter the marketplace to better cater to those participants. Starting new sport programs, however, presents significant challenges, including acquiring and mobilizing resources in innovative ways. Using theory in sport development and the resource-based view, the authors examined six emergent sport programs for girls within the United States and United Kingdom to identify the resources obtained and mobilized to create new and distinctive sport opportunities in a crowded marketplace. Following a case study approach, data from site visits and interviews with 137 individuals were analyzed using within- and across-case analysis. The findings reveal the resources needed to grow the programs, the ways in which those resources are attained, and strategies to mobilize resource bundles to maximize sport opportunities by differentiating programs from traditional, mainstream sport opportunities. The findings also highlight the distinctive opportunities and challenges for sport organizers in both top-down and bottom-up sport development systems. This study informs theory in sport development and provides insight for creatively designing and delivering sport opportunities that expand overall sport participation for adolescent girls.