Goal difference
Goal difference, goal differential or points difference is a form of tiebreaker used to rank sport teams which finish on equal points in a league competition. Either "goal difference" or "points difference" is used, depending on whether matches are scored by goals (as in ice hockey and association football) or by points (as in rugby union and basketball). Goal difference is calculated as the number of goals scored in all league matches minus the number of goals conceded, and is sometimes known simply as plus–minus. Goal difference was first introduced as a tiebreaker in association football, at the 1970 FIFA World Cup, and was adopted by the Football League in England five years later. It has since spread to many other competitions, where it is typically used as either the first or, after tying teams' head-to-head records, second tiebreaker. Goal difference is zero sum, in that a gain for one team (+1) is exactly balanced by the loss for their opponent (–1). Therefore, the sum of the goal differences in a league table is always zero (provided the teams have only played each other). Goal difference has often replaced the older goal average, or goal ratio. Goal average is the number of goals scored divided by the number of goals conceded. It was replaced by goal difference, which was thought to encourage more attacking play, encouraging teams to score more goals (or points) as opposed to defending against conceding. However goal average is still used as the tiebreaker in Australian rules football, where it is referred to as "percentage". This is calculated as points scored divided by points conceded, and then multiplied by 100. If two or more teams' total points scored and goal differences are both equal, then often goals scored is used as a further tiebreaker, with the team scoring the most goals winning. After this a variety of other tiebreakers may be used. (Wikipedia).
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