Wallop was the author of ten novels and Baseball: An Informal History. But his most famous book is The Year the Yankees Lost the Pennant (1954), a humorous update of the Faust legend in which the devil apparently helps the Washington Senators in the AL race. At the last moment, of course, the devil turns out to be a secret Yankee fan who has set up the Senators for a heartbreaking near-miss, and the hero must choose between saving his soul or winning the pennant for Washington. The book was turned into the long-running Broadway musical and movie, Damn Yankees.