"A Man Saw a Ball of Gold in the Sky" can be interpreted as a Naturalistic poem. The movement called Naturalism, a movement which includes Stephen Crane, reveals the humanity of experiences and emotional states of common lowly characters. With this definition in mind, the reader of Crane's poem may be able to infer that when the man "achieves the ball of gold" and "It was clay," the man's experiences and commonness only allow him to perceive clay, rather than gold. For the forces such as heredity and environment have kept his thinking downward: When he is in the sky and looks down upon the ball, he sees clay since it is no longer unattainable ("in the sky").
But, when he returns to the earth, the ball, now gazed at from the dark harshness of life that the Naturalists perceive, appears gold, for again it is unattainable. Crane goes on to write,
Now this is the strange part:/It was a ball of gold/Aye, by the heavens, it was a ball of gold.
This last line, "by the heavens," carries two possible meanings: (1) It is an expression and (2) it means that perceived by the heavens--not the common, lowly man--the ball is gold. Afterall, for many "perception is reality" as Dean Kuntz wrote in one of his novels. Certainly, the Naturalists have a dark, skeptical, and at times pessimistic view of things.