This chapter is concerned with unsanctioned, malicious violence in the form of foul or dirty play and the psychological processes which lie behind such acts. It begins with a brief return visit to the problems of differentiating between sanctioned and unsanctioned aggression and violence and the grey areas that exist and which can sometimes cause difficulty in distinguishing between the two. The focus here moves to the importance of players’ rules or norms as well as the rules of the particular sport. Following this, further discussion of intimidation and retaliation, beyond the points raised in chapter 4, are explored in relation to unsanctioned aggression and violence. The discussion also examines those athletes, sometimes known as ‘athletic psychopaths’, whose acts of unsanctioned violence are deliberately calculated to attempt to start trouble or injure players by unprovoked violent attacks on opponents. Finally, the motivation behind the behaviour of athletic psychopaths as well as other forms of unsanctioned violence will be explored using reversal theory and Apter’s (1997) categories of violence.