AmerginLiath
Adventurer
Sumo, is, and always has been, a sport. From a philosophical point of view, it would be like having a pro-footballer class.
You could do a monk subclass which emphasises grappling, but I think I would call it something else.
I think that this raises the question of how 5e should approach martial arts styles beyond either coming up with new Monk traditions or letting the player describe how they’re fighting/grappling. Should there be feats that provide new options of attack/defense/stance? Should a few new Battlemaster maneuvers be created that work with grappling or weaponless fighting (thus allowing another character to take them via Martial Adept)? Previous editions came up with different subsystem solutions — dating back to 1e’s OA — some working better than others, to describe martial arts styles and schools outside of the usual attack progression (and as more than just “this is the Monk class”). Does the 5e system have proper tools to naturally build the same?