The Chicago Cubs, improbably, were riding a nine-game winning streak on Sept. 14, 1953, facing the first-place Brooklyn Dodgers for the second game of a two-game set. The home-field Cubs would beat the Dodgers again that day to make it 10. Overall, though, it was a miserable season for the Cubs, and the game wasn’t memorable for anyone, specifically, on the field that day. Instead, it was notable, seven decades later, for the middle infielders watching from the bench — men who played key roles, some of them long forgotten, in the history of baseball’s integration, and thus in the history of the United States. Chicago Cubs Manager Phil Cavaretta, center, with his two new shortstops, Gene Baker, left, and Ernie Banks, upon their arrival at Wrigley Field, Sept. 14, 1953. (Bettmann/Getty Images) Jackie Robinson,...