Denny McKnight had a significant impact on the early years of professional baseball, despite his relatively short career. He was a key figure in the formation and development of the American Association, which was a major league that rivaled the National League in the 1880s and 1890s.

McKnight's involvement in baseball began in Pittsburgh, where he was a prominent local businessman. He was one of the founders of the Allegheny Baseball Club of Pittsburgh in 1876, which later became the Pittsburgh Pirates. He served as the club's first president and was instrumental in its early success.

In 1881, McKnight was one of the driving forces behind the creation of the American Association. He was dissatisfied with the National League's high ticket prices and strict rules, and he believed that a new league could offer a more accessible and enjoyable experience for fans. The American Association was founded with these principles in mind, and it quickly gained popularity.

McKnight served as the first president of the American Association, and he was a key figure in its early years. He helped to establish the league's rules and structure, and he was involved in many of its most important decisions. He was also the owner and manager of the Pittsburgh Alleghenys, one of the league's founding teams.

Despite his significant contributions to the American Association, McKnight's time in baseball was relatively short. He left the league in 1882, after just one season as president. He sold his interest in the Alleghenys in 1883, and he was not involved in professional baseball after that.

However, McKnight's impact on the sport was lasting. The American Association was a major force in baseball for a decade, and it played a key role in the development of the modern game. Many of the innovations that McKnight championed, such as lower ticket prices and a more fan-friendly approach, are still important parts of baseball today.

In recognition of his contributions to the sport, McKnight was posthumously inducted into the Pittsburgh Pirates Hall of Fame. Despite his brief career, he left a significant legacy in baseball and is remembered as one of the sport's early pioneers.