This study qualitatively examined the motivationally relevant behaviors of key social agents in specializing sport participants. Seventy-nine participants (9-18 years old) from 26 sports participated in semi-structured focus groups investigating how coaches, parents, and peers may influence motivation. Using a critical-realist perspective, an inductive content analysis indicated that specializing athletes perceived a multitude of motivationally relevant social cues. Coaches' and parents' influences were related to their specific roles: instruction/assessment for coaches, support-and-facilitation for parents. Peers influenced motivation through competitive behaviors, collaborative behaviors, evaluative communications, and through their social relationships. The results help to delineate different roles for social agents in influencing athletes' motivation.