Sport fans develop unique and engaging relationships with their favourite sport teams, both offline and online. However, research on sport fan engagement is still limited in relation to social media. The purpose of this research is to understand why and how sport fans engage with clubs on social media. Following the Uses and Gratifications approach and the Consumers' Online Brand-Related Activities framework, seven motivations (Information, Entertainment, Personal Identity, Integration and Social Interaction, Empowerment, Remuneration and Brand Love) and three dimensions of online engagement behaviours (Consumption, Contribution and Creation) were considered. A web-based survey was conducted among football club fans of a major UEFA league on Facebook, resulting in 562 responses. The need for Information, Empowerment and Brand Love mainly drive Consumption, Contribution and Creation, respectively, while the need for Integration and Social Interaction emerged as the second most important motivation overall. This study contributes to the emerging research on social media use in the sport marketing literature, thus revealing additional opportunities for managers to engage their fan base online.