The aim of this paper is to examine the basis of eligibility rules in sport by exhibiting the logic of categorisation, with its associated ethical problems. We shall be concerned mainly with pre-competition categories - age, sex, weight and dis/ability - because they are directly relevant to sports performance and are relatively stable inequalities. We shall prefer to use the term "categorisation", although we mean by it just what others might mean by classification, to refer to divisions, classes, groups, etc. The paper argues that we have categories only because we consider it desirable to offer some groups protected status in order to enable and promote inclusion and fairness. This desirability condition determines eligibility. Only then do issues arise of which sub-categories we should have, and how they are to be policed. There will always be categories in sport, as a minimum to protect athletes based on age groupings, from children to veterans. But since every categorisation brings its own problems, we need to ensure that we keep them balanced, so that sport can strive for maximum inclusion of different kinds of athletes, and maximum fairness. This requires us to step back from the many particular debates in order to rethink the logic of the whole categorisation process.
Keywords: Philosophy; categorisation; disability sport; ethics; policy; sex.