The paper deals with the problem of how people handle random events. Many accounts of the chance element in games and many attempts at general explanations of gambling assume that the actor accepts the events as unpredictable and passively awaits the outcome. A study of people playing roulette in a gaming club suggests that this is far from the case. Playing roulette can be seen as an exercise in `skill' which depends upon the construction and maintenance of predictive theories. One form of theorizing attributes causal efficacy to the croupier and the game becomes a contest between croupier and player. This is reinforced by the croupiers as they attempt to manipulate their working conditions and status. Players may then adopt a non-arithmetic calculus of win and loss which confirms their theorizing. Losses are the `entrance fee' to a public entertainment, whilst wins are evidence of a successful working strategy.