Wonderboy, Roy's bat, is symbolic on two levels. On the first and more superficial level, Wonderboy is clearly a stand-in for a sword, like Arthur's Excalibur, that grants its user special powers. When using Wonderboy, Roy is able to hit bad pitches; without it, his bad habit gives him problems. On a deeper level, both Wonderboy and Excalibur are phallic symbols. Nowhere is this more obvious than during Roy's slump, when Wonderboy "sags like a baloney." But in the presence of Iris Lemon—the "vegetative goddess" who causes a man near her to feel a sexual urge—Wonderboy snaps back to hardness, and Roy is able to hit again. Wonderboy is a symbol of Roy's masculine strength, and it is strongest when he is with the woman who gives him the most strength and support, his proper mate.
When we first see Roy, he is on a train in a tunnel. The emergence of the train from the tunnel is an image of birth; indeed, Roy is being born, at age nineteen. He is still a child, a country bumpkin spilling things on himself and completely unsure of how to act. The train later returns whenever Roy becomes frightened, symbolizing his desire to return to the womb. He thinks of the train during his slump. Perhaps more significant, he thinks he hears the train when Iris presses him about taking responsibility for his role as both a player and a man.
As mentioned above, the playing field is a clear stand-in for the Waste Land. The field is dry and parched when Roy arrives, but after his first hit, rain falls for three days and turns the field a vibrant green once more.