Sustainability in sport depends on internal operations and how teams and organizations engage fans, sponsors, participants, and communities in shared environmental values. Our stakeholder engagement research blends social identity theory, framing theory, and strategic communication models to understand what messaging and initiatives resonate across diverse audiences. Through surveys, interviews, and experimental methods, we evaluate the effectiveness of green campaigns, fan-facing behavior change programs, and sponsor activations. The goal is to produce actionable insights that help organizations meet environmental and marketing objectives—enhancing loyalty, trust, and social impact while advancing climate goals and helping drive new revenue streams.