Answer: The close relationship between sumo wrestlers could be an incentive for an elite wrestler to throw a match he doesn’t need to win.
In this excerpt, the author tells us that sumo wrestlers have extremely close relationships. The pool of elite sumo wrestlers is extraordinarily tight-knit. Moreover, each wrestler belongs to a stable, and stables often have rivalries between them. Therefore, the author argues that the close relationship between sumo wrestlers might be an incentive for a wrestler to throw a match he does not need to win.