In 1890 the Reds won the Players' League pennant when they finished first ahead of the New York Giants, and then won the American Association pennant when they finished first ahead of the St. Louis Browns (now the Cardinals). The Boston Reds are one of two major league teams to win back-to-back pennants spanning two different leagues. The Brooklyn Dodgers did it also, winning the AA pennant in 1889 and the NL pennant in 1890.
At the conclusion of the 1891 season, the National League pressed for the consolidation of the American Association with the National League. Part of the posturing included the National League directing its champion Boston Beaneaters not to play the Reds in a World Series. The leagues settled, adding four AA clubs to a combined circuit. As part of the settlement, the owners of the four clubs not joining the combined circuit, including the Reds, were paid $135,000 and their players dispersed to the surviving clubs.
Their abandoned ballpark was revived for use by the National League club in 1894, during the weeks that South End Grounds was being rebuilt following a fire. The Congress Street Grounds, with its close left field foul line, quickly gained some more history, as Bobby Lowe hit four home runs in one game there, the first player to accomplish that feat.