Sport categorization is often justified by benefits such as increased fairness or inclusion. Taking inspiration from John Rawls, Sigmund Loland’s fair equality of opportunity principle in sport (FEOPs) is a tool for determining whether the existence of an inequality ethically justifies the institution of a new category in any given sport. It is an elegant ethical normative framework, but since FEOPs does not account explicitly for athlete safety (i.e. athlete physical and mental wellbeing), we are left in an ethically dubious (...) situation where the risk of harm associated with a categorization regime might in fact prove to be greater than the risk of harm present within the sport before its introduction. To address this critical gap, I propose the ‘scales of ignorance’ ethical normative framework to weigh the relative risk of harm within a sport, crucially inserting athlete safety into the discourse surrounding ethical justification for categorization in sport. The current paper is the first explicit formulation of assessment and ethical justification of risk of harm in the familiar logic of FEOPs. The scales of ignorance framework can also be used independently of Loland’s approach. Two new concepts are also proposed: ‘insidious risk of harm’ and ‘pernicious risk of harm’. (shrink)