TOKYO (Reuters) – Grand champion Harumafuji has informed Japan’s sumo association of his intention to retire, an association spokesman said on Wednesday, after his assault of a junior wrestler tainted the image of the national sport just as it was regaining popularity.

“Yokozuna” (grand champion) Harumafuji, 33, apologized earlier this month after media reported he had beaten junior wrestler Takanoiwa while drinking with at a restaurant bar with other wrestlers.

Harumafuji was angered when he saw the younger wrestler checking his smartphone after being chastised for having a bad attitude, the reports added.

The incident has highlighted the struggle of the ancient sport to reform the harsh conditions that can breed violence in its closed, hierarchical world, although some wrestlers say there have been improvements in the decade since a teenage wrestler was beaten to death by other wrestlers.

A Japan Sumo Association spokesman said on Wednesday that Mongolian Harumafuji’s “oyakata” Isegahama, who runs the gym, or “stable”, where he trains, had informed the JSA of his decision on the grand champion’s behalf.

The head of an advisory body to the JSA, the Yokozuna Deliberation Council, had said on Monday the affair warranted “extremely harsh punishment” but did not issue a final decision because both the JSA and police were still investigating.

“There is almost no doubting that an act of violence was carried out,” Masato Kitamura, chairman of the advisory body, told a news conference after a council meeting on Monday.

“The general feeling within the council is that a strict disciplinary measure is required,” he added.

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 from his injuries.

Mongolian yokozuna Asashoryu quit the sport that same year after a probe into reports of a drunken scuffle in Tokyo.

The incidents and competition from rival sports had eroded the popularity of the sport, in which giant wrestlers clad in loin-clothes seek to topple or push each other out of the ring.

But the promotion in January of Japan-born wrestler Kisenosato to grand champion status, the first home-grown yokozuna in 19 years, had helped rebuild its fan base.

Harumafuji, one of the many Mongolian wrestlers who have come to dominate the sport in recent years, started his career in Japan at the age of 16 and was promoted to “yokozuna” in 2012. He has won nine grand tournaments in all.