As we await to see how the Kyokai deals with this (they said it will be dealt with after the basho) some news:
According to the Daily Shincho tabloid, the incident occurred at a drinking party attended by members of the supporters' club. A man known as a major sponsor attended the event with a woman, and it is said that a drunk Hakunofuji became rude and harassed the woman. This angered the sponsor. Isegahama Oyakata also became enraged and punched Hakunofuji. The punch must have been so powerful that Hakunofuji's face was swollen and he could not even open his eyes.
Side note: Currently, Isegahama beya is based in a five-story apartment building in Sumida Ward, but plans are reportedly underway to build a new heya in the Ryogoku area. It is an ambitious plan with total construction costs said to be in the region of 2 billion yen, but progress is running slower than initially expected, and the Oyakata is said to have been growing increasingly impatient. Following the temporary closure of Miyagino beya and the merger of the two heya, Isegahama beya has become the largest heya with 31 wrestlers, after Miyagino assault incident The Kyokai will likely have a difficult time dealing with this incident.