I looked up some stuff about history from the NFL website but frankly I'm not sure my audience has much overlap with football fans.
Still, this note stuck in my mind:
1904 - Halfback Charles Follis signed a contract with the Shelby (Ohio) AC, making him the first known black pro football player.
This would help explain why in the 1934 Middletown, Ohio yearbook ("The Optimist"), there are several African-American players.
Bear in mind, Arizona schools were still segregated by race at that time. :P
Two more, relevant to the 1920s:
1920 - Pro football was in a state of confusion due to three major problems: dramatically rising salaries; players continually jumping from one team to another following the highest offer; and the use of college players still enrolled in school. A league in which all the members would follow the same rules seemed the answer.
(They called themselves the American Professional Football Association; soon to become the NFL)
1921 - At the league meeting in Akron, April 30, the championship of the 1920 season was awarded to the Akron Pros.
A) The Akron team getting the title at a meeting in Akron? That sounds more crooked than the BCS (thanks, Bill!)
B) Isn't it nice that in just a few hours we'll know the champion once and for all? That's great if you love football, and also great if you don't love football. No offense, but I don't want to be hearing MORE football news in April.
1922 - The American Professional Football Association changed its name to the National Football League, June 24.
--From the 2010 NFL Record & Fact Book via the NFL website