The Agallian Base Ball Club was the first formally organized baseball team at Wesleyan University. It was formed in the autumn of 1864 and played its first matches against other teams the following spring. Baseball had been played informally at Wesleyan back to at least 1860. Baseball letters were given (often at a considerably later date) to Wesleyan athletes in baseball beginning with the 1861-62 season. The name Agallian was given by professor of Greek James Van Benschoten as a derivation of the name Agalles, who was said to have invented the first game of ball-playing in ancient Greece (cf. College Argus, June 11, 1868).

The club played its first match against the Charter Oak Base Ball Club of Hartford in the spring of 1865, losing 22-12. Its first intercollegiate game, which was also Wesleyan’s first intercollegiate athletic contest, was against Yale on September 30, 1865, with Yale winning 39-13. One of club’s founders, Charles L. Bonnell, class of 1868, served as captain for his entire playing career. The first practices and home games took place on the Washington Street green in Middletown and on a nearby vacant plot of land on Washington Street. Later photos exist of games being played on the Wesleyan campus on what is now Andrus Field, which at the time was essentially an undrained swamp or wetlands. The Agallian club was not a formally sponsored university team but a club composed of members of several Wesleyan classes. A later organization, the University Base Ball Club, founded in 1869, seems to have had a more formal endorsement from the administration.

The Agallian B.B.C. ceased to function after 1871, when baseball began to be eclipsed by the popularity of rowing as a collegiate sport. Aside from informal contests between class teams, Wesleyan was not to have an organized baseball program again until 1888.