The 1902 Pittsburgh Pirates won a second straight National League pennant, by an overwhelming 27.5 game margin over the Brooklyn Superbas. It was the Pirates' first ever 100-win team, and it remains the franchise record for best winning percentage at home (.789).

John Dwight Chesbro was an American professional baseball pitcher. Nicknamed "Happy Jack", Chesbro played for the Pittsburgh Pirates (1899–1902), the New York Highlanders (1903–1909), and the Boston Red Sox (1909) of Major League Baseball (MLB). Chesbro finished his career with a 198–132 win–loss record, a 2.68 earned run average, and 1,265 strikeouts. His 41 wins during the 1904 season remains an American League record. Though some pitchers have won more games in some seasons prior to 1901, historians demarcating 1901 as the beginning of 'modern-era' major league baseball refer to and credit Jack Chesbro and his 1904 win-total as the modern era major league record and its holder. Some view Chesbro's 41 wins in a season as an unbreakable record.