Host residents’ support is of paramount importance for the success of spectator sports events. Factors influencing event support have been investigated in past research, but usually in isolation. The current study includes multiple factors by analysing the relationship among involvement, social impact experiences, and event support. Data were collected online four and six months before, during, and two months after the 2021 UCI Road World Championships from 3219 from residents, representative for the city of Leuven (Belgium). The 2021 UCI Road World Championships offered a unique context, as it was the first large spectator sports event organised in Flanders since COVID-19. The event had a limited social impact, but this increased over time (e.g., community spirit and event support). Social impact experiences mainly exerted a significant influence on event support rather than attitudinal and behavioural involvement factors. The results of this study inform national and local policymakers to attract events, event organisers to achieve impact and legacy, and other scholars to improve the understanding of spectator sports event research.