Yorozu asserts that Force/0 = Infinite if a force is applied to any of its contact regions since they are infinitesimally zero. And as a result, according to Newton's Third Law, the reaction force applied to you would be unlimited/infinite/undefined. It is not possible to touch or grasp at an infinitely small point because of math and quantum mechanics. Real objects never have absolute rigidity at the macro level, and they have some flexibility to spread out the region.
You can try it on
this calculator for example area= 0 and force= 1 (infinity)
The reason its High 3-A is because anything that comes in contact the perfect sphere will also be subjected to the infinite pressure as well hence hit with High 3-A levels, thats why when it comes in contact with the ground it complete and perfect erases everything in its path and not does not leave a scratch, crack, burn... etc
Now, in terms of scaling, no one but Yoruzo's perfect sphere will have High 3-A