Grand champion Harumafuji's retirement over his assault on another wrestler was seen by many Japanese as inevitable, a consequence of his failure to live up to the dignity any yokozuna must show.

But the 33-year-old Mongolian sumo star's exit should not be considered "case closed," as the sumo world faces the daunting task of ridding itself of violence and restoring an image already tarnished by past scandals.

Speaking at a press conference Wednesday, Harumafuji said he would quit sumo to "take responsibility as a yokozuna" for injuring lower-ranked wrestler Takanoiwa at a bar in western Japan last month during a regional tour.

He argued that he had been trying to fulfill his outside-the-ring duty to teach his fellow Mongolian wrestler manners, but admitted that he "took things a bit too far."

Some sources close to the matter have said Harumafuji was angered by Takanoiwa attempting to use his smartphone while being scolded for bad behavior by another Mongolian yokozuna, Hakuho, who was also at the scene.

"Harumafuji's retirement was unavoidable. But the Japan Sumo Association should not draw a curtain on this problem...its crisis management panel should continue its investigation, find out the real problem and make improvements," Masayuki Tamaki, a sports critic, said.

Some fear the latest incident indicates that violence may have taken root in the world of Japan's traditional sport.

"Violence is the exact opposite of courtesy. Even if Harumafuji wanted to teach manners to Takanoiwa, using violence was the wrong way to do it," novelist Atsuko Asano said.

Asano recalled the fatal hazing of a 17-year-old wrestler in 2007. His stablemaster argued at the time that the excessive exercise blamed in part for the teenager's death was done for the purpose of discipline and "was appropriate because it was aimed at developing his strength and skills."

"If there is something in common between the assault (in 2007 and Harumafuji's case), the Japan Sumo Association must work on this problem hard, or the same thing can happen again. The association is facing a crucial test," she said.

Questions have also emerged over the association's tepid initial response to the scandal.

Even after the association learned about the assault from the police, it initially thought it was a quarrel between stables and individuals and did not act promptly. Detailed investigations started only after the media began reporting the case earlier this month.

Further complicating the issue was Takanoiwa and his stablemaster Takanohana's mysterious behavior. Takanohana filed a police report before notifying the association, and both he and Takanoiwa have remained tight-lipped over the incident.

Takanohana also did not allow Takanoiwa to be questioned by the association, hampering the progress of the investigation. Takanohana is believed to hold a grudge against the association's current chairman, Hakkaku, after he was defeated in last year's election to pick sumo's new head.

Another sports expert, meanwhile, called for revisiting the way a yokozuna is chosen, given that it is not the first time that the holder of sumo's highest rank has been involved in an assault incident.

In 2010, then grand champion Asashoryu, another Mongolian, allegedly seriously injured a male acquaintance in a drunken rampage. He announced his retirement soon afterwards.

Noting that the current thinking is that yokozuna must have "good spirit, technique and physical condition to fight," Hidenori Tomozoe, a professor of Waseda University's Faculty of Sport Sciences, said the criteria are "too focused on technique and physical condition."

Tomozoe also said "preaching" to wrestlers about avoiding violent incidents would likely not bring changes to their mindset.

"To make respectable sumo wrestlers, I rather think they should take part in social contribution activities -- such as serving at care facilities for the elderly and the disabled when they are young," he said.

Learning about socially vulnerable people could be important for wrestlers, especially because they live in a world where the strong traditionally prevail, he said.