While some sports (such as fishing or hiking) have been viewed as primarily recreational, most sports are considered competitive. The majority involve competition between two or more persons (sometimes using horses or cars). For example, in a game of basketball, two teams compete against one another to determine who can score the most points. When there is no set reward for the winning team, many players gain a sense of pride. In addition, extrinsic rewards may also be given. Athletes, besides competing against other humans, also compete against nature in sports such as whitewater kayaking or mountaineering, where the goal is to reach a destination, with only natural barriers impeding the process. A regularly scheduled (for instance annual) competition meant to determine the "best" competitor of that cycle is called a championship. Baseball is a competitive sport. Professional sports, as well as the business of it, are intense and extremely competitive, while recreational sports are often less intense and found enjoyable by many, as well as cathartic. Yet psychological evidence has been found that the more aggressive sports result in increased aggressive behavior when the sport is not being played. For those attaining winning status, endorphins are released, often driving them, and in extreme cases, addicting them to increased levels of c
mpetition, dedication, and enjoyment of the sport. In the case of sports viewers, participating artificially, similar evidence was found. Mostly in professional sports rivals, there may be half of the home team's fans and half of the visiting team's fans viceversa during the rivalry games. Competitive sports are governed by codified rules agreed upon by the participants. Violating these rules is considered to be unfair competition. Thus, sports provide artificial (not natural) competition; for example, competing for control of a ball, or defending territory on a playing field is not an innate biological factor in humans. Athletes in sports such as gymnastics and competitive diving compete against each other in order to come closest to a conceptual ideal of a perfect performance, which incorporates measurable criteria and standards which are translated into numerical ratings and scores by appointed judges. Sports competition is generally broken down into three categories: individual sports, such as archery; dual sports, such as doubles tennis, and team sports competition, such as cricket or football. While most sports competitions are recreation, there exist several major and minor professional sports leagues throughout the world. The Olympic Games, held every four years, is usually regarded as the international pinnacle of sports competition.