This article contributes to ongoing debates about trends in violence in sport through an examination of the emergence of Mixed Martial Arts (MMA). The article counters suggestions that the rise of MMA is indicative of a decivilizing and/or de-sportizing process, arguing instead that the development of MMA can best be explained with reference to the concepts of informalization and the ‘quest for excitement’. More particularly, the article argues that MMA emerged as a global sport as a consequence of the ascendancy of professionalism over amateurism, through a hybridization of Eastern and Western combat styles, and due to participants’ desires to generate increased levels of excitement. The article argues that despite academic and public portrayals to the contrary, considerable self-restraint characterizes the violence in MMA. The sport has, however, oscillated between more and less violent forms as relatively ‘de-sensitized’ participants and wider public lobbies have contested the definition of socially tolerable violence. In order to maintain spectator appeal under increasingly stringent regulation promoters have sought to make ‘cosmetic’ changes to MMA to increase the appearance of de-controlled violence. The article concludes by arguing that combat sports are inherently contentious as they necessarily exist close to the boundary between ‘real’ and ‘mock’ fighting and thus on the margins of modern sport.