A greater understanding of the mechanisms underpinning motivation for team sport during adolescence, a period when search for identity intensifies, is necessary to promote sport involvement amidst declining rates of participation. This study explored factors underpinning Irish adolescents' motivation to participate in team sport. Six gender-specific focus-group discussions were conducted with 40 athletes (21 males and 19 females) aged 11 to 16 years from three Gaelic sport community clubs in Dublin, Ireland. Thematic analysis revealed four themes that underpinned adolescents' team sport motivation: 'Desire for Competence', 'Opportunity to Experience Relatedness', 'Transformational Leadership Style', and 'Gendered Expectations and Identity'. The first two themes, 'Desire for Competence', and 'Opportunity to Experience Relatedness', reflected the basic needs participants perceived as crucial to their sport motivation. The sport team context facilitated opportunities for identity formation through perceptions of belongingness with other team members, which was a key driver of youth sport participation. The third theme, 'Transformational Leadership Style' represented a key mechanism through which these basic needs were facilitated. The final theme 'Gendered Expectations and Identity' exposed a gendered lens through which motivation can be understood in the Irish adolescent team sport context. Identification with a sports team may be particularly important to enable girls to establish gender role expectations that incorporate athleticism. In this manner, teammates can contribute to healthy identity development, a central task of the young person's development. Drawing on self-determination theory and identity theory, the findings extend our understanding of the way in which social processes influence adolescents' distinct motivations to participate in team sport.