Very reminiscent of the sumo wrestling chapter in Freakonomics. Here's a Wikipedia summary:

"One striking example of the authors' creative use of economic theory involves demonstrating the existence of cheating among Sumo wrestlers. In a Sumo tournament, all wrestlers compete in 15 matches and stay in the top league if they win at least 8 of them. The Sumo community is very close-knit, and all of the wrestlers at the top levels tend to know each other well. The authors looked at the final match, and considered the case of a wrestler with seven wins, seven losses, and one fight to go, fighting against an 8-6 wrestler. Statistically, the 7-7 wrestler should have a slightly below even chance, since the 8-6 wrestler is slightly better. However, the 7-7 wrestler actually wins around 80% of the time. Levitt uses this statistic and other data gleaned from Sumo wrestling matches and the effect allegations of corruption have on match results, to conclude that those who already have 8 wins collude with those who are 7-7 and let them win, since they have already secured their place in the league."

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