Fighting in a boxing style is the most spectacular behaviour of red kangaroos,  Macropus rufus, yet its structure and function have not been analysed in detail. Patterns of sparring, kicking and wrestling occur between mothers and young (especially males), in formalized contests between males, and in escalated conflicts over resources (shelter, water, oestrous females). Observations were made of fighting behaviour in free-living and captive individuals. The frequency of fighting between various age/sex classes in the field was determined and the structure of fighting over a water resource was analysed from a 12 h videotape record. These results were compared with an analysis of 85 videotaped plus 35 other fights observed in a captive group of eight males (age 1 - 7 year). These fights were formalized contests  which did not involve or resolve any immediate conflict over a resource. Such fights share many of the properties ascribed to play-fighting. They are initiated with invitational behaviour that does not include characteristic threat behaviour seen in fights over a resource. They involve self-handicapping, some lack of dominance distinctions, and usually several bouts occur interrupted by mutual pauses. The structure of the fight suggests that the main goal is to push or wrestle the opponent off balance and down to the ground rather than inflict potentially injurious kicks as seen in resource conflicts. Furthermore larger opponents often adopt an inferior flat-footed stance and dominants and/or winners kick significantly less than losers. The  context, goals and structure of these non-resource based fights suggest that they are a form of play-fighting. Selection of play partners on the basis of size/dominance or kinship indicate that such play-fighting in red kangaroos is neither truly cooperative nor disruptive and selfish. The behaviour most likely functions as a form of non-damaging assessment of opponents with benefits in skill development in younger individuals.