This paper explores the relationship between rugby union and the demography of religion in Ireland over the first five decades of the game's development on the island. Rugby in Ireland underwent a transition in this period from a game dominated by Protestants in terms of playing numbers and positions of power to one with a mixed religious composition. This paper will examine this transition taking into account such factors as class, politics and social change. Rugby, as a rich reservoir of social capital, had considerable attractions for the emerging Catholic middle classes.