Almost all his life Jack Kerouac had a hobby that even close friends and fellow Beats like Allen Ginsberg and William S. Burroughs never knew about. He obsessively played a fantasy baseball game of his own invention, charting the exploits of made-up players like Wino Love, Warby Pepper, Heinie Twiett, Phegus Cody and Zagg Parker, who toiled on imaginary teams named either for cars (the Pittsburgh Plymouths and New York Chevvies, for example) or for colors (the Boston Grays and Cincinnati Blacks).

He collected their stats, analyzed their performances and, as a teenager, when he played most ardently, wrote about them in homemade newsletters and broadsides. He even covered financial news and imaginary contract disputes. During those same teenage years, he also ran a fantasy horse-racing circuit, complete with illustrated tout sheets and racing reports. He created imaginary owners, imaginary jockeys, imaginary track conditions.

All these “publications,” some typed, some handwritten and often pasted into old-fashioned composition notebooks, are now part of the Jack Kerouac Archive at the Berg Collection of the New York Public Library. The curator, Isaac Gewirtz, has just written a 75-page book about them, “Kerouac at Bat: Fantasy Sports and the King of the Beats,” to be published next week by the library and available, at least for now, only in its gift shop.

Mr. Gewirtz said recently that he had included much of the fantasy material in a 2007 Kerouac exhibition he mounted at the library, and had planned to add a chapter about the fantasy sports in the catalogue but ran out of space. “I’m glad I waited,” he said, “because it forced me to go into it all in much more depth.”