The classic is Catcher With a Glass Arm, but any number of Matt Christopher's original sports fictions for young readers are delightful. Some sample copy:
Catcher With a Glass Arm: "Just when he thinks he'll spend the rest of the season on the bench nursing his weak throwing arm, Jody learns what it takes to come through in a pinch."
The Kid Who Only Hit Homers: "When a mysterious man promises to make him a great player, Sylvester accepts and begins a phenomenal home-run streak."
Look Who's Playing First Base: "Mike Hagin offers his new friend from Russia the first baseman's position on the little league team before he finds out the boy can't play baseball."
There's more where those came from, folks--over a hundred more, according to an unnamed source. And it's not just baseball--Christopher covered all sports. And the books still sell at a price that is just right for the impoverished shopper.