Sportsman, Businessman, the son of Harry Cooke Cushing III, a financial adviser from an old Boston family, and of the former Cathleen Vanderbilt, a descendent of the railroad magnate Cornelius Vanderbilt, who was known as Commodore Vanderbilt. Harry Cushing IV had what he called polo-mania. He was an active amateur player in the 1950's, 1960's and 1970's, mostly in Rome, where he kept his eight polo ponies, and elsewhere in Europe and in Asia. He lived in Rome from the mid-1950's to about 1985. He wrote in his recently finished memoirs, ''I witnessed both the birth and the death of Rome's 'Dolce Vita.' Occasionally, he also played polo at the Meadowbrook Polo Club in Old Westbury, N.Y., which was the center of the polo world from the 1920's to the early 1950's. In the winter, he sometimes played in the old Squadron A Armory on 94th Street between Park and Lexington Avenues. In the polo world, players' levels of skill range from the lowest, called an A handicap, to the highest, a 10-goal handicap. Mr. Cushing had a 5-goal handicap, which is very good for an amateur, said Al Bianco, a friend who is chairman of the Meadowbrook club. Mr. Bianco said Mr. Cushing ''could hit a good long ball, and he was very, very aggressive and very self-assured'' on the polo field. A polo team has four players, and Mr. Cushing used to hire three professionals to join him to play in Europe or the United States. The level of skill of his teammates varied according to the skill level permitted in whatever tournament they were playing. The teams he put together in Rome won many trophies, Mr. Bianco recalled. When his teams played in the United States, he sometimes shipped his own ponies over from Rome. Mr. Cushing was born in Manhattan and graduated from Avon Old Farms School, a boarding school in Avon, Conn., where he became skilled in polo. He attended Cornell before joining the Army after Pearl Harbor. During World War II he was a cryptographer at the Pentagon and in the South Pacific.