This paper explores the interaction of informal constraints on human behaviour by examining the evolution of English football jerseys. The jersey provides an excellent setting to demonstrate how informal constraints emerge from formal rules and shape human behaviour. Customs, approved norms and habits are all observed in this setting. The commercialisation of football in recent decades has resulted in these informal constraints, in many cases dating back over a century, co-existing with branding, goodwill and identity effects. Combined, these motivate clubs to maintain the status quo. As a result, club colours have remained remarkably resilient within a frequently changing landscape.