Official Site of the National Football League
Basic American Football Rules
NFL season: A glossary of terms and football jargon you'll need to fit in
Blocking (American football) - Wikipedia
History- May 14, 1874 How Canada created American football – RCI
9 Facts About Football In The First World War
Early history of American football - Wikipedia
The NFL, the NCAA, and the Eternal Football Rules Debate - The Ringer
20 Football Facts: History, Popularity, Rules & More
American Football League (AFL), History, Joe Namath, & Teams