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.