Each ball, when released, will fall toward the center of the big ball that everybody is standing on.
Another way to describe it: Each ball, when released, will fall in the direction parallel to a line from the boy's head to his feet.
-- The ball held by the boy on top will fall toward the bottom of the picture.
-- The ball held by the boy on the right will fall toward the left side of the picture.
-- The ball held by the boy on the bottom will fall toward the top of the picture.
-- The ball held by the boy on the left will fall toward the right side of the picture.
In each case, the direction toward the center of the big ball that they're all standing on is the direction that each person calls "down".
