Sportsmanship is a bit vage notion about behaving in a decent, moral, friendly, gracious, respectful way on and around the board.
Wikipedia describes it as:
Sportsmanship expresses an aspiration or ethos that the activity will be enjoyed for its own sake, with proper consideration for fairness, ethics, respect, and a sense of fellowship with one's competitors. Being a "good sport" involves being a "good winner" as well as being a "good loser".
Sportsmanship typically is regarded as a component of morality in sport, composed of three related and perhaps overlapping concepts: fair play, sportsmanship and character. Fair play refers to all participants having an equitable chance to pursue victory and acting toward others in an honest, straightforward, and a firm and dignified manner even when others do not play fairly. It includes respect for others including team members, opponents, and officials. Character refers to dispositions, values and habits that determine the way that person normally responds to desires, fears, challenges, opportunities, failures and successes and is typically seen in polite behaviors toward others such as helping an opponent up or shaking hands after a match. An individual is believed to have a "good character" when those dispositions and habits reflect core ethical values. An example of poor sportmanship is exemplified in a team's calling timeouts to run up the score on an opponent when the former team already has a sizeable lead.
Sportsmanship can be conceptualized as an enduring and relatively stable characteristic or disposition such that individuals differ in the way they are generally expected to behave in sport situations. In general, sportsmanship refers to virtues such as fairness, self-control, courage and persistence and has been associated with interpersonal concepts of treating others and being treated fairly, maintaining self-control in dealing with others, and respect for both authority and opponents.
Our colleagues at Chess describe it as
The players shall take no action that will bring the game of chess into disrepute. It is forbidden to distract or annoy the opponent in any manner whatsoever. This includes unreasonable claims, unreasonable offers of a draw or the introduction of a source of noise into the playing area. (FIDE - Laws of Chess article 12.1 and 12.6)
Sportsmanship is therefore culturally defined (what in one country is seen as normal is in an other country offensive.)
Sportsmanship can be seen as what makes a game enjoyable for all players.
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