At some point in the early 1900s, Agar immigrated to the United States from his native England. In 1905, he founded his first team, Critchleys. In 1906, he was instrumental in the founding of the New York Amateur Association Football League. Agar was elected as the league's secretary, a position he held until at least 1911. He was also president of the league in 1910. In January 1909, Agar broke his leg while challenging for the ball. He remained with Critchleys until it folded following the 1912–13 season. He then played at least one season, 1916–17 with New York Clan MacDonald of the New York State Association Football League and at least one season, 1919–20 with Longfellows of the New York State League.
Referee
Agar also served as a referee for the New York Amateur Association League, being assaulted while officiating a game in April 1910.
USFA
While Agar was part of the founding of the United States Football Association in 1913. However, he later became one of the major forces opposing the USFA during the 1928–1929 "Soccer War."
In 1922, Agar entered the realm of professional team ownership when he entered the Brooklyn Wanderers into the American Soccer League. The ASL was set for its first season and the Wanderers would play at Hawthorne Field, a dedicated soccer facility owned by Agar. Agar also chose to manage the team and played several games during the team's first two seasons. In 1926, Hakoah Vienna, one of the top Austrian teams toured the U.S. The team was composed entirely of Jews, many of whom were favorably impressed with the United States. Agar, who was also Jewish, immediately began negotiations to sign the players and in December 1926, brought the several Hakoah stars to the Wanderers. Despite the additional talent, the Wanderers remained a mid-table team for much of its existence.
Southern New York State Football Association
During the Soccer War, the USFA brokered the creation of the Eastern Soccer Leaguecomposed of three teams suspended from the American Soccer League as well as several teams from the Southern New York State Football Association. The SNYFA considered the ESL to be encroaching on its territory, and, when the association president, Dr. Manning, resigned, Agar was elected in his place. Agar then led the SNYFA in leaving the USFA and allying itself with the ASL against the USFA.
In June 1926, Agar was selected to coach the U.S. national team in a two-game, home and away, series with Canada. The U.S. lost the first, 1–0, in Canada, but won the November rematch 6–1, in the U.S. On June 11, 1926, Agar again led the U.S. to a 6–2 victory over Canada.
