A sport consists of a normal physical activity or skill carried out under a publicly agreed set of rules, and with a recreational purpose: for competition, for self-enjoyment, to attain excellence, for the development of skill, or some combination of these. The difference of purpose is what characterises sport, combined with the notion of individual (or team) skill or prowess.

Examples of skills which have become sports:

• Gladiators in Rome fought and killed for the delectation of the audience, rather than to protect the Empire:
• Yachting is the travel across water for enjoyment or competition rather than e.g. for transport or commerce:
• Running is done on a course for a fixed length of time or distance, rather than simply to catch a bus.

Physical sports use characteristics such as strength, stamina, speed, dexterity and other skills, other sports use more cerebral skills (see mind sport), such as strategic thinking in chess. This article, however, will concentrate on physical aspects of sport.

The line between sports, games, exercise and play is certainly not clear; games are often redefined as sports when they involve particularly skilled participants, which gives them appeal to non-participants. This is especially true in the modern age, which gives much weight to the spectator aspect of sports. Similarly, play is usually understood as less purposeful activity, but can become more like a game or sport as it conforms more to external rules or patterns of behaviour. Exercise is action to develop skill or ability, and may be a forerunner of both sport and games.