© 2020 Elsevier Ltd Rationale and objective: Unhealthy, energy-dense nutrient-poor foods and beverages are heavily promoted through sport sponsorship. This naturalistic trial assessed whether exposing young adult spectators to various types of counter-advertising (CA) before watching an unhealthy food sponsored elite sporting event could diminish sponsorship effects and increase support for restrictions on sponsorship. Method: Young adults (ages 18-29 years) who planned to watch the Australian Football League (AFL) Grand Final were recruited through an online panel and randomly assigned to one of four conditions: (A) control (neutral advertisement); (B) anti-industry CA (critiquing unhealthy food industry sponsorship of sport); (C) anti-product CA (critiquing the association of sports stars with unhealthy food); or (D) negative health effects CA (highlighting negative health consequences of unhealthy food consumption). Participants (N = 1316) completed a pre-test questionnaire and viewed their assigned CA online 1–3 days before watching the 2017 AFL Grand Final, which featured unhealthy food sponsorship. Results: Participants who reported watching the AFL Grand Final (n = 802) answered post-test measures within five days of the event. Results indicated that participants found the anti-industry CA more believable, attention-grabbing, reassuring and encouraging than the anti-product CA. The anti-industry CA promoted less favourable attitudes to sponsor brands, the anti-product CA promoted reduced intentions to purchase the fast-food sponsor brand, and the negative health effects CA reduced preferences for fast food in general compared to the control condition. Conclusions: Anti-industry CA may detract from favourable attitudes to unhealthy food sponsor brands and negative health effects CA may detract from intentions to consume fast food in the face of unhealthy food sponsorship exposure. Such interventions may require higher dosage levels than applied in the present study to bolster spectators’ resistance to the surfeit of unhealthy food sport sponsorship.