[1][2] In 2002, Steven Levitt and Mark Duggan published a paper using econometrics in order to suggest that corruption in sumo exists.
[3] Popularized in Levitt's book Freakonomics, the study found that 70% of wrestlers with 7–7 records on the final day of the tournament (i.e., seven wins and seven losses, and one fight to go) won.
When the former sumo wrestler Kōnoshin Suga, also known as Onaruto stablemaster, and his supporter Seiichiro Hashimoto came forward with allegations of match rigging, drug use, sexcapades, tax evasion, and close ties to the Yakuza, both were found dead in the same hospital, hours apart on April 14, 1996, though there was no proof of poisoning.
[6][8] In September 2008, Wakanohō, a wrestler who had been expelled for cannabis use, claimed he was forced to accept bribes to forfeit sumo matches.
In February 2011, Japan's Ministry of Education, Culture, Sports, Science and Technology and National Police Agency announced that an investigation into allegations of baseball gambling by sumo wrestlers and officials had discovered cell phone text messages indicating that some matches had been fixed.
Three wrestlers, Chiyohakuhō, Kasuganishiki (who had recently retired to become a coach under the elder name Takenawa), and Enatsukasa, reportedly admitted to throwing or fixing bouts.
[6][13] As a result of the independent investigation, the board of directors of the Japan Sumo Association (JSA) decided in an extraordinary meeting to cancel the March 2011 tournament in Osaka.
[16] Uncovering the problem is made even more difficult by the existence of a separate form of collusion ("koi ni yoru mukiryoku-zumo" in Japanese, meaning deliberate lack of effort in a sumo bout), which refers to a rikishi going lightly on an opponent without the exchange of money.