Background <p>Few United States youth meet physical activity (PA) guidelines, with notable gender, racial/ethnic, and geographic disparities. Sport is one of the best strategies for increasing PA levels, yet girls drop out at a higher rate than boys, and both rural and Hispanic girls participate in lower numbers than their counterparts. Physical literacy (lifelong ability to move) and sport sampling (multiple sport engagement) are core elements of healthy youth sport participation. Commonly cited barriers to starting and/or sustaining sport participation include lack of competence (feeling capable), autonomy (feeling independent), and relatedness (feeling connected to others), in line with self-determination theory (SDT). Unique cultural factors also influence PA and sports participation among Hispanic girls. The proposed research aims to determine the feasibility of an out-of-school sport sampling and physical literacy intervention (Girls PLAY) on rural, Hispanic girls’ PA levels.</p> Methods <p>For Aim 1, we will conduct qualitative interviews (<i>n</i> = 37) with rural-dwelling girls, parents, coaches, and program staff to identify sport participation determinants for rural, Hispanic girls and use these findings to inform Girls PLAY program development. For Aim 2, we will optimize the program using human-centered design (HCD) strategies such as live prototyping. Staff will implement the program for 2&#xa0;weeks at a time to a program site, with feedback collected via direct observation and interviews. Feedback will inform additional program modifications. For Aim 3, we will determine the feasibility of the modified program. Staff will deliver the Girls PLAY program using SDT-based instruction at two out-of-school programs. In a sample of thirty girls, we will examine feasibility (recruitment, assessments completed, acceptability, appropriateness, attendance) and pre-post changes in PA, physical literacy, and sport participation, as well as theorized program mediators of SDT constructs.</p> Discussion <p>This study’s innovative use of HCD strategies will help culturally tailor the Girls PLAY intervention components and ground this work in knowledge about the rural, predominantly Hispanic border populations and the contexts in which it will be delivered. This work is significant in that addressing barriers to physical activity and sport via an out-of-school program can reduce gender, racial, and geographic disparities in youth activity levels.</p> Trial registration <p>ClinicalTrials.gov, NCT06229457, registered January 11, 2024, <a href="https://clinicaltrials.gov/study/NCT06229457">https://clinicaltrials.gov/study/NCT06229457</a>.</p>