Where did New York City get its "Big Apple" nickname from?

New York City's famous nickname is widely credited to 1920s sports journalist John J. Fitz Gerald. In horse racing, a "Big Apple" referred to the rich prize money available at the sport's most prestigious tracks, many of which were in New York City. After hearing stable hands use the term to describe the city, Fitz Gerald adopted it in his newspaper column, helping popularize the phrase. The nickname experienced a major revival in the 1970s when New York City's tourism bureau embraced "The Big Apple" in a highly successful marketing campaign.