Cities are full of disputes about organizing public life. These disputes are important for deciding how spaces get used, and they are integral to how publics form and develop. In all sorts of ways they define the potentialities of urban public life. This article tells the story of the Southbank Centre’s plans to redevelop their central London site, and Long Live Southbank’s protest of these plans to save their skateable space. Through this detailed case study the article develops a distinctive conceptual apparatus for making sense of public disputes. Drawing links between Deweyan pragmatism and assemblage theory, the article explores how publics were drawn together as assemblages of humans and non‐humans with the capacity to act and argue. It follows the arguments that each side made—and the justifications underpinning them—to explore the different ideas of public‐ness that were at stake in the disagreement. This also helps highlight the space for cooperation that existed. The article emphasizes the part affect played in shaping the dispute; recognizing its role in public reasoning, and in how people get pulled into different publics. This is a story not only of disputation, but of how a corner of London expanded its public‐ness.