Wonderboy has a mythic backstory. Roy made it from wood from the heart of a tree that was struck by lightning. It glows so blindingly white that pitchers complain about it. It's like magic:
Wonderboy flashed in the sun. It caught the sphere where it was biggest. A noise like a twenty-one gun salute cracked out of the sky. There was a straining, ripping sound and a few drops of rain spattered to the ground. (3.97)
Not only does Wonderboy literally rip the cover off the ball, but like the lightning that made it, starts a rainstorm and ends a drought. Two droughts, that is—the drought of rain that's plagued the ball field and the drought of wins.
Roy hits so well that the managers can't help but think that the bat's been doctored somehow. As long as Roy stays true to his quest for success, Wonderboy works its magic. When he sells his soul and agrees to the fix, disaster strikes. Wonderboy splits in half after Roy smacks a foul ball. Without it, he can barely finish the at-bat and takes a called third strike. He doesn't even lift his bat.
And speaking of bats that go up or don't, Malamud wrote that Wonderboy had many meanings, but that an important one was as a phallic symbol, a symbol of Roy's male potency. Sometimes Roy holds Wonderboy high up above his shoulders. But at one at-bat during his slump, "Wonderboy resembled a sagging baloney." (6.125) At that moment, the mysterious lady in the seats stands up and Wonderboy rises to the occasion for a home run.
With all the lightning imagery, you could think of Wonderboy as a lightning bolt and think of Roy as Zeus hurling the thunderbolt in the iconic representation of the god. When Roy whacked the cover off the ball in that towering homerun, it was like lightning struck. It rained for three days, another symbol of how Roy had the power to bring the team back to life.
Last but not least. Wonderboy reminds lots of lit scholars of Excalibur. You know—the sword that King Arthur pulled out of the stone when he was a boy and showed that he should be the next king. Here's what Thomas Malory wrote in 1469 in his famous book Le Morte D'Arthur (The Death of Arthur): "Then he drew his sword Excalibur, but it was so bright in his enemies' eyes, that it gave light like thirty torches." Sound familiar?
So he blazed away for her with his golden bat. It was not really golden, it was white, but in the sun it sometimes flashed gold and some of the opposing pitchers complained it shone in their eyes. (4.19)
BTW, "Roi" means "King" in French. Coincidence? We think NOT!
Regardless of which imagery you like best, you have to admit that Wonderboy is a pretty manly symbol. It's not for nothing that after Roy "dies" at his final at-bat, he lovingly buries Wonderboy in the ballpark after the game. He's lost his career, and he's lost Memo, the two things that represented his self-image as a man. The author tells us that "it was a smooth, clean break, as if the bat had willed its own brokenness […]" (11.1) Almost like Roy.