Previous physical activity interventions have failed to create population change and an alternative approach is needed to support a World Health Organization target of a 15% reduction in global levels of inactivity by 2030. There is growing evidence that gamification-based interventions can reach substantial portions of the community. However, to date, these studies have been predominantly quantitative and as such there is a paucity of research in the area on motivations and barriers to engagement with these programs. Four focus groups conducted with N = 26 players who participated in a gamification-based intervention 'Beat the Street' revealed several varied motives to engagement, including collective reward; social influence; game reinvention; exploration; accessibility and awareness. However, several barriers specific to the Beat the Street intervention and outdoor gamification interventions more generally were also identified. This study provides novel insight into the motives which engage individuals into physical activity interventions and the design principles which need to be considered when implementing interventions of this nature.