A mix of soccer and rugby, the early version of American football was popular at colleges but not so for those who turned pro. This was also a very violent sport - so bad and deadly (you read that right!) that a sitting US president considered banning football unless changes were made.
What were the early rules? Why was the field of play called a "gridiron." Check out the names and types of offenses (single wing, T-Formation, etc.) and who the founders were - and why many of them were against professional football (aka post-graduate football).