That any life should be lost during sport is tragic, and sumo is no exception.
Had Takashi Saito decided not to enter the world of professional sumo, he probably would still be alive today. Instead, in late June, after a particularly brutal period of butsukari-geiko (a training routine in which a senior, and usually heavier, opponent is pushed across the ring), apparently coupled with physical abuse from his elders, Saito collapsed. He was taken to a hospital where he died a few hours later. A member of Tokitsukaze Beya, one of sumo's more prestigious heya in terms of history and sekitori output, he was known as Tokitaizan.
At least one police investigation is underway yet no concrete conclusions on accountability can be drawn from comments to date, bar the fact that Saito was physically (and probably mentally) abused. Undoubtedly maltreated, he died having endured the unendurable, all the time while under the supposed care of experienced stable master Tokitsukaze Oyakata.