Roogie writes the coach of the Dodgers, telling him about his power. A fictional coach reads the letter to real Dodger players Campanella, Hoes, Erskine and Meyer. They all have a good laugh. Roogie gets two tickets for a game, catches a foul ball and throws it back to Campy who tumbles back into the dugout because of the power of the throw. Roogie gets a contract but at the end of the season when he tries to pitch the Dodgers to the pennant, his bump disappears. He becomes the team's mascot and the Dodgers win the pennant.
Acting wise it's not a very good movie. The kid who plays Roogie never acted in another movie again, but he's not bad, I've seen worse kid actors. The Dodgers players are a bit stiff but clearly enjoy the experience. Campanella is the only one who gives a good performance. The other actors are of no importance. There is the beginning of a love story between Roogie's widowed mother and the Dodgers coach. The story is a bit slow, there is much talk about exploiting the kid just to earn a buck and too little actual baseball.
The scenes of games we see are stock footage, which is okay because we see Ebbets Field in it's glory days, Jackie Robinson at bat and a roaring crowd. There's a sound of a crowd cheering looped over and over and once you notice it gets on your nerves.
Conclusion: fun for Dodger fans to see some of the boys of summer act. Other than that there is no reason to watch it.