Young people aged 11 to 17 often fail to meet global recommendations for weekly physical activity and sports (PAS), despite its numerous benefits. In Spain, challenges such as excessive technology use and disinterest in PAS are prominent among youths. This study aimed to analyse the interest in PAS during leisure time and identify the factors influencing young people in a Spanish municipality towards this practice, as well as establish differences according to age and gender. Involving 891 adolescents (429 girls, 432 boys, and 30 other genders), this study found a significant association between gender and PAS participation. Boys are mainly motivated by fun and fitness, girls by health and fun, and other genders by perceived sports competence and health, with these motivations increasing with age. Deterring factors include fatigue, laziness, and lack of enthusiasm across all groups. Lack of free time is the most cited reason for quitting PAS, particularly for girls and other genders. For boys, disinterest, especially between ages 13 and 15, is a primary reason. These findings suggest that promoting PAS with a focus on health and leisure, and tailoring programmes to gender and age-specific needs, are essential to maintain motivation and ensure a healthier, more active population.