ABSTRACT Research question The competitive landscape facing branded running events demands insights into how to increase brand loyalty amongst participants. This study examines how participants need to engage with branded running events to stimulate brand loyalty; and how the social environment (i.e. the presence of other unacquainted participants), encourages participants to engage more with the event brand. Research methods Data, collected via personally administrated survey, from 246 participants of the closing event of ‘Cairo Runners' were analysed by means of Partial Least Squares Structural Equations Modelling. Results and findings Self-brand identification is enhanced by cognitive, behavioural and emotional engagement with the event brand. To encourage Word-of-Mouth requires emotionally and socially engaged participants. As a social stimulus, perceived similarity with other unacquainted participants acts as a major driver of social, behavioural and cognitive engagement. Positive perception of other participants’ physical appearance stimulates cognitive and emotional engagement but hinders social engagement. Suitable behaviour of other participants encourages social engagement. Implications Theoretically, this is the first study on participatory sport events including the full spectrum of participant engagement with an event brand; highlighting the unique role the different ways of engagement play in stimulating aspects of brand loyalty. The findings quantify the largely overlooked stimulus effect created by the sheer presence of unacquainted participants on participant engagement. We highlight the central role of perceived similarity amongst participants as a driver of participant engagement. Event organisers are encouraged to identify alternative criteria that resonate with participants to create a sense of similarity amongst participants.