The poem begins as a simple game. The speaker throws a ball up, down and against a wall, and it always returns, which seems to please him. The tone is light, almost childlike, with that cheerful "Hey!" when the ball bounces back.
Then the mood shifts. Tired or bored, the speaker flings the ball to the floor, and it rolls into a corner, "despondent." He slumps in a chair and watches it. Now the ball seems to have feelings of its own, looking back at him "sullen." It glows red and takes the shape of his heart, and it seems to scold him for refusing to "play ball with life."
The ball works as a mirror. Its mood is really his, and the poem suggests he feels guilty or regretful about giving up on life's give-and-take. The ending is quiet and self-accusing, with a hint that the game might still be picked up again.