There were 10 charter teams of the American Professional Football Association that began play in 1920. The APFA changed its name to the National Football League in 1922. Click on the 'Charter Teams of the NFL' link on this page to read about them.
Amazingly, one, the Cincinati Red Stockings, who became the Reds began play as the only National Association Ball club in 1869.
20. There were 10 teams in the American League and the Mets and Astros were the 9th and 10th teams in the National League.
At first there was only one team and that was the New York Nickaboppers and they played for free.
There are currently 30 teams.