.....I know that grand sumo will try to hype this victory as Shishimaru's endurance/resilience drove Katsumi to quit because he wouldn't stay down regardless.... but the rest of squad sumo will likely not see it the same way... and again in the tradition of Raiden we get to see a kick delivered and a kick held back. This is so a reference to the conclusion of Round 5 of another manga.
It's incredible how smoothbrains are filtered by this conclusion. Do you think jack lost against sikorsky because he left the arena ?
It's a perfect call back of katsumi vs doyle, where katsumi abandonned a easy and obvious victory for the sake of his mind. He fight for fun, not for "muh winning"