Harvard later challenged its closest rival, Yale, to which the Bulldogs accepted. The two teams agreed to play under a set of rules called the "Concessionary Rules", which involved Harvard conceding something to Yale's soccer and Yale conceding a great deal to Harvard's rugby. They decided to play with 15 players on each team. On November 13, 1875, Yale and Harvard played each other for the first time ever, where Harvard won 4–0. At the first The Game (as the annual contest between Harvard and Yale came to be named) the future "father of American football" Walter Camp was among the 2000 spectators in attendance. Walter, who would enroll at Yale the next year, was torn between an admiration for Harvard's style of play and the misery of the Yale defeat, and became determined to avenge Yale's defeat. Spectators from Princeton also carried the game back home, where it quickly became the most popular version of football.