"The result is that Pop has the feeling he has been jinxed since the time of his flop, and he has spent twenty-five years and practically all of his pile trying to break the jinx, which he thinks he can do by making the Knights into the world champs that the old Sox never did become." (2.184)
Baseball is full of superstitions, and the jinx is one of the most powerful ones. Pop has worked out some sort of deal in his head with the baseball gods, which would let him break the jinx inaugurated by Fisher's Flop and finally get some good luck.
Doc Knobb's hypnotism cut down their jitters but it didn't much help their coordination, yet when they were left unhypnotized for a few days, they were afflicted with more than the usual number of hexes and whammies and practiced all sorts of magic to undo them. To a man they crossed their fingers over spilled salt, or coffee or tea, or at the sight of a hearse. (3.84)
One of the coolest things in The Natural is its use of all the superstitious jargon from baseball, like jinxes, hexes, and whammies. This passage shows how the players seem to make their own luck; when they're hypnotized they are focused and play all right, but without Doc Knobbs' treatment they get caught up looking for new rituals and end up screwing up even more. They believed that the hypnosis helped, and that's what mattered.
In the locker room Pop asked Roy to explain why he thought the cover had come off the ball.
"That's what you said to do, wasn't it?"
"That's right," said Pop, scratching his bean.
This is one of those weird moments in the novel where it seems like Roy has some supernatural powers to make his thoughts come true, but only on the baseball field.
"Some have said maybe [Bump's death] wouldn't happen if you didn't join the team, and maybe so, but I believe such things are outside of yours and my control and I wouldn't want you to worry that you had caused it in any way."
[. . .]
Roy felt uneasy. Had he arranged Bump's run into the wall? No.
This exchange between Pop and Roy is almost funny, if it weren't so morbid, because while they say, over and over, that Roy didn't cause Bump's death, they're actually revealing that they think that he might have. Of course Roy didn't "arrange" Bump's bump, but he did kind of wish for it, so we get another hint that Roy has some pretty powerful brain waves.
Gus pointed to his glass eye. "The Magic Eye," he said. "It sees everything and tells me." (4.195)
We don't know if Gus is telling the truth about his glass eye, but we also don't want to stick around to find out. He does seem to have an ability to know what other people are thinking are doing, which makes him a very successful gambler. The point isn't whether it's really the eye that tells him, but that he makes other people believe that it's magic, giving him a creepy aura. And that's a psychological advantage for a schemer.
Lola finally came in with a Spanish shawl twisted around her. She lit up the crystal ball, passed her gnarled hands over it and peered nearsightedly into the glass. After watching for a minute she told Roy he would soon meet and fall in love with a darkhaired lady.
"Anything else?" he said impatiently.
Lola looked. A blank expression came over her face and she slowly shook her head. (6.58-60)
Roy's quick encounter with Lola the fortune-teller is another brush with the supernatural, and she actually gets things partially right. Roy does meet a dark-haired lady, Iris, but it's hard to say whether or not he falls in love with her. What's really strange is the way that the future just seems to turn off the lights for Lola. It might mean that Roy isn't destined for anything, that the future's up to him. But he doesn't act like it.
He practiced different grips on Wonderboy before his bureau mirror and sewed miraculous medals and evil-eye amulets of fish, goats, clenched fists, open scissors, and hunchbacks all over the inside of his clothes. (6.65)
No, he's not getting ready for a Halloween party; Roy's trying to break his slump by using every lucky charm he can find or invent in combination with trying to change up his swing. The collection of crazy objects he sews into his clothes shows us just how desperate he is for a little help from the baseball spirits. He's trying everything, including practicing (which probably will have the greatest effect).
A white shadow flew into the bathroom. Rushing in, he kicked the door open. An ancient hoary face stared at him. "Bump!" He groaned and shuddered. An age passed… (6.77)
The ghost of your ex-enemy showing up in your bathroom? This happens while Roy's in his hitting slump, so we can read the ghost as a sort of comparison he's making between himself and his successful, but dead, competitor. Bump's ghost might also be making an appearance to scare (or warn?) Roy away from Memo.
And though Fowler goose-egged the Cubs in the last of the ninth and got credit for the win, everybody knew it was Roy alone who had saved the boy's life. (6.134)
You've heard stories like this before, about sick kids asking their favorite sports figures to shoot a basket or hit a homer for them. Well, this time Roy's in the hot seat for a sick boy, and when he breaks his slump and gets his homerun, everyone takes for granted that the boy's saved somehow by the healing powers of baseball. It might be that the request from the boy's desperate Dad motivated Roy to break the slump, but he doesn't see it that way; he thinks it was Iris.
"I was jinxed," Roy explained to her. "Something was keeping me out of my true form. Up at the plate I was blind as a bat and Wonderboy had the heebie jeebies. But when you stood up and I saw you with that red dress on and thought to myself she is with me even if nobody else is, it broke the whammy." (7.58)
Like we said, Roy thinks that Iris was the key to breaking his slump. He talks about being jinxed and having a whammy, words that Pop associates with Memo. Sure enough, it was his date with Memo that started Roy's slump. But seeing a woman in the stands who believes in him, which is precisely what Memo doesn't give him, is what gave Roy the confidence to get a hit.