Book excerpt: Propounding his "small ball theory" of sports literature, George Plimpton proposed that "the smaller the ball, the more formidable the literature." Of course he had the relatively small baseball in mind, because its literature is formidable--vast and varied, instructive, often wildly entertaining, and occasionally brilliant. From this bewildering array of baseball books, Ron Kaplan has chosen 501 of the best, making it easier for fans to find just the books to suit them (or to know what they're missing). From biography, history, fiction, and instruction to books about ballparks, business, and rules, anyone who loves to read about baseball will find in this book a companionable guide, far more fun than a reference work has any right to be.