Bad food and overpriced drink had been sold at ballparks since the 1850s. But it took one very ambitious British-born caterer to turn concessions into an empire. Harry M. Stevens had begun his career hocking scorecards in the 1880s, all the while regaling the crowds with quotes from Byron and Shakespeare. By 1901 he was peddling hard-boiled eggs, ham sandwiches, ice cream, and slices of pie in stadiums from New York to Ohio. Then, one cold afternoon when ice cream sales slowed at the Polo Grounds, he sent out for German sausages, which he put in long buns so fans could hold and eat them. He had made his greatest contribution to the game, introducing hot dogs to the ballpark.
From "Inning 2: Something Like a War (1900-1910)" in Ken Burns' Baseball