It needs to be said but punching a rikishi in the gut is going to do jack shit.
They're massive beasts with immense walls of abdominal muscle and a thick armour of body fat to cushion surface blows and the good ones are deceptively agile on their feet with years of training against guys strong enough to do some real damage with palm slaps.
Naruse getting in that close would have got squelched by the big lad.
But weight classes don't mean much in manga...