[1] A right-handed batter and thrower, Duffy was listed as 5 feet 7 inches (1.70 m) tall and 168 pounds (76 kg).

[3] Duffy entered the National League with Cap Anson's Chicago White Stockings in 1888 after receiving an offer of $2,000 from the club.

During his time with Boston, Hughie and Tommy McCarthy forged a reputation as the celebrated “Heavenly Twins” outfield of the early 1890s.

During the 1902 and 1903 seasons, Duffy was player-manager for the Western League's Milwaukee Creams franchise.

He moved to the Milwaukee Brewers of the American Association in 1912, but he was fired after a season in which the team struggled.

[9] He turned down an offer to manage the 1913 St. Paul Saints, saying that he was hoping to work in the east.

In 1921, Duffy was hired as full-time manager of the Red Sox, guiding them for two seasons.

Duffy remained on the Red Sox' scouting staff nearly to the end of his life, retiring in 1953.

[13] In 2019, Duffy was inducted into the Ivan Allen Jr. Braves Museum and Hall of Fame, along with Terry Pendleton.