The Japan Sumo Association (JSA) in Tokyo announced on Wednesday Harumafuji's decision to retire.
The wrestler's "oyakata" stablemaster, or gym manager, Isegahama said Harumafuji "has caused great trouble to the association and the public" and that he bears responsibility. A grand champion's behavior is expected to be exemplary in sports and in society.
Japanese media reported two weeks ago that Harumafuji hit another Mongolian wrestler, Takanoiwa, in the head at a party in October fracturing his skull and causing other injuries.
The younger wrestler had apparently angered the grand champion by checking his smartphone after being reprimanded for his bad attitude. The winner of nine grand tournaments, Harumafuji allegedly struck Takanoiwa with his palms, fists and a karaoke machine remote control.
The 33-year-old Harumauji apologized for the incident which happened at a restaurant bar where other wrestlers were present.
Strict rules of behavior
The JSA imposes strict rules on wrestlers who are required to live in communal sumo training stables where tradition dictates all aspects of their daily lives.
Japan is the only country where the wrestlers are professionals. Sumo's origins stretch back centuries and its traditions have links to Japan's Shinto religion. The large wrestlers wear loin-cloths and seek to topple or push their opponents out of the ring.
The association is conducting an investigation, but Harumafuji decided to retire before it takes place.
Harumafuji was born Davaanyam Byambadorj and made his debut in 2001. His most recent victory was at the autumn tournament in September. He was promoted to yokozuna, the sport's highest rank, in 2012.
The reputation of sumo has been damaged by a number of scandals in recent years, although it was beginning to recover ahead of this latest incident. In 2011, the Spring Grand Sumo Tournament was canceled after 14 wrestlers were accused of match-fixing.
In 2010, another Mongolian grand champion Asashoryu, announced his retirement following reports that he injured a man while drunk.
A former oyakata was sentenced to five years in prison in 2010 after a court found he had ordered wrestlers to beat 17-year-old trainee Takashi Saito, who had tried to run away, in 2007. Saito died as a result of his injuries.
The 31-year-old Kisenosato has become the first Japanese wrestler to rise to grand champion status in 19 years. This had led to an increase in popular support for the sport.
jm/sms (AP, Reuters)