Arena Football League
Following the successes of his trial-run games, Foster moved ahead with his idea for arena football. He founded the Arena Football League with four teams: the Pittsburgh Gladiators, Denver Dynamite, Washington Commandos, and Chicago Bruisers. Foster appointed legendary Darrel "Mouse" Davis, godfather of the "run and shoot" and modern pro offenses, as executive director of football operations. Davis hired the original coaches and was the architect of the league's original wide-open offensive playbooks.

Q: How many teams did the Arena Football League originally have?
four