ATP rankings

The ATP Rankings, as defined by the Association of Tennis Professionals (ATP), are the "objective merit-based method used for determining qualification for entry and seeding in all tournaments for both (male) singles and doubles, except as modified for the ATP World Tour Finals (singles or doubles)." The rankings period is "the immediate past 52 weeks, except for: Barclays ATP World Tour Finals, singles and doubles, which is dropped on the Monday following the last ATP World Tour event of the following year; Futures Series tournaments that are only entered into the system on the second Monday following the tournament's week. Once entered, all tournaments, except the Barclays ATP World Tour Finals, remain in the system for 52 consecutive weeks."

The ATP began as the men's trade union in 1972 and rose to prominence when 81 of its members boycotted the 1973 Wimbledon Championships. Just two months later, in August, the ATP introduced its ranking system intended to objectify tournament entry criteria, which up to that point was controlled by national federations and tournament directors.

The ATP's new ranking system was quickly adopted by men's tennis. While virtually all ATP members were in favor of objectifying event participation, the system's very first No. 1, Ilie Năstase, lamented that "everyone had a number hanging over them," fostering a more competitive and less collegial atmosphere among the players.

The original ATP ranking criteria, which persisted through the 1980s, was based on averaging each player's results, though the details were revised a number of times. Starting in 1990, in conjunction with the expansion of ATP purview as the new men's tour operator, the ranking criteria was replaced with a 'best of' system modeled after competitive downhill skiing. This 'best of' system originally used 14 events but expanded to 18 in 2000.

A player's ATP Ranking is based on the total points he accrued in the following 19 tournaments (18 if he did not qualify for the ATP World Tour Finals):

The requirement to play in four ATP World Tour 500 events does not apply to a player who was outside the top 30 in the previous year-end ranking; however, no more than four of his results from 500 level events may be counted. For a better result within the same tour type to be transposed one has to wait for the expiry of the first worse result from previous year. It only expires at the drop date of that tournament and only if the player reached a worse result or hasn't entered the current year.

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