The 1870 college football season is considered to be the second season ever played of intercollegiate football competition. Much like in the first year, 1869, the rules were still considered in flux, and were decided on in a game-to-game basis. However, the rules used likely did not resemble anything that a modern football observer would recognize, being that of a mix of soccer and rugby.
As in 1869, there were only 2 games played for the entire season; however, there was a third team, Columbia University, that played in addition to the previous year's Rutgers and Princeton teams. The first game of the year was a 6-3 Rutgers win over Columbia on Rutgers' campus played on November 5, and the second game of the year was a 6-2 win of Princeton over Rutgers on Princeton's campus on November 12.
Therefore, as the only team without a loss for the year, Princeton is generally considered to have won the college football national championship for play in the 1870 season. The Tigers have been so recognized by the Billingsley Report, the National Championship Foundation, and college football research historian Parke H. Davis (among others) with that honor. Princeton was also the first-ever undefeated team, finishing with a 1-0 record.