Play fighting in rats is used to show how the four principles can be used to characterise the organisation of the behaviour and then select behavioural markers that can be scored numerically. The partners compete to access the nape of each other’s neck and the behaviour patterns used during these encounters are derived from adult sexual encounters. Body size and agility can affect which tactics are used as can the location in the enclosure in which an encounter takes place. Taking these factors into account reveals that some actions cannot be explained as being compensatory to either gaining or avoiding nape contact. This, in turn, reveals novel aspects of organisation of play fighting and leads to identifying novel behavioural markers to measure those aspects of organisation.