TOKYO >> Mongolian grand champion Harumafuji has decided to retire from sumo after allegations that he assaulted a lower-ranked wrestler and tarnished the image of Japan’s national sport.

Harumafuji’s stablemaster Isegahama announced the grand champion’s retirement on Wednesday. He said that Harumafuji “has caused great trouble to the association and the public” and that the grand champion bears responsibility.

Harumafuji allegedly struck Takanoiwa with his palms, fists and a karaoke machine remote control at a drinking party in late October, fracturing his skull and causing other injuries.

The Japan Sumo Association, which imposes strict rules on wrestlers, is conducting an investigation, but Harumafuji decided to retire ahead of the probe.

The news has dominated Japanese television talk shows and evening newspapers for weeks as the nation expressed shock at claims against a yokozuna grand champion, whose behavior in sports and society is expected to be exemplary.

Born Davaanyam Byambadorj, Harumafuji debuted in 2001 and has won the championship nine times, with his most recent victory at the autumn tournament in September. He was promoted to yokozuna, the sport’s highest rank, in 2012.

Harumafuji’s retirement is the latest scandal to rock the sumo world.

In 2011, the JSA decided to cancel the Spring Grand Sumo Tournament after revelations that 14 wrestlers were involved with match-fixing.

In 2010, grand champion Asashoryu, also of Mongolia, announced his retirement following reports that he injured a man while intoxicated.