Confused with pressure in closed-box

kbuild

I'm confused when i consider about this picture in my head.

... imagine that there is a ''closed-box'' on the floor.
And ball A is in this closed-box.
Pressure acted on the box = Patm.

I'm wondering, how much pressure act on ball A ?

With my sense, i think it is Patm.
... but i can't explain! it's a closed-box, so air mass above the box should have no effect on the ball in box ?!

Doc Al

If the box is rigid and sealed from the surrounding air, then the outside pressure shouldn't affect the ball inside.