The Power of Belief is a supernatural force in this verseThe more famous someone becomes, and the more people believe in them, the greater the people believed in become. There are three candidates for this.
1. Babe Ruth.He says it himself, "Legends never die". So many people knew of him, and so many believed him to be "less than a god but more than a man" that he became just that. That dream Benny had was no dream; Babe Ruth is now a Spirit Advisor for baseball players.
2. BennyThe feats he accomplishes are improbable and amazing. "Only a few guys in history ever busted the guts out of a ball." Originally he was merely a good player, but then the power of belief built up. "You're the best on the team! You don't need to practice." The belief of his team and that snooby team made him into a demi-god. Smalls unintentionally became his prophet of sorts by spreading the fame of "The Rocket".
3. The BeastUntil the climax, we don't see the Beast/Hercules himself. We only hear growls from the darkness. This plus the yard and the legend led the kids to believe that the Beast is some kind of supernatural monster. One that can bite through wood easily, twist metal poles into knots and become much bigger than a typical English Mastiff. Once Benny conquers his fear by jumping into the Beast's lair, the dog shrinks to a more mundane size. Then by outrunning the Beast, the other kids lose their fear as well.