Mental toughness (MT) enables individuals to thrive in demanding situations; however, current conceptualizations of MT are primarily based on research with elite adult athletes. Thus, the purpose of the current study was to explore youth sport coaches’ perceptions of mentally tough adolescent athletes with whom they have worked. Phenomenological interviews were conducted with 14 youth sport coaches (nine men and five women). Using a hermeneutic process, a thematic structure comprising five themes was developed: (a) Youth athletes demonstrate their MT by overcoming various obstacles, (b) mentally tough youth athletes are highly self-determined with respect to their sport participation, (c) mentally tough youth athletes control their emotions in competition, (d) mentally tough youth athletes focus on aspects that facilitate their performance, and (e) mentally tough youth athletes are good teammates. These findings not only complement existing conceptualizations of MT but also highlight important distinctions in the manifestation of the construct in early to middle adolescents.