[quote author=Dave in Fairfax link=topic=40456.msg2268611#msg2268611 date=166864615
...the evolution of American football from what was essentially a version of rubgy (I can't remember if it was union or league)
It was league. League is the dominant form of the game, in Northern England, so even in my early days of NFL I could see the similarities. What really transformed the game called American Rugby League into American Football was the introduction of the forward pass, by the QB.
FWIW, the reason that American Football has the forward pass has to do with efforts to decrease the violence of the game during the early 20th century. There were 2 proposals being kicked around - one was to widen the field to spread the players and the other was to allow the forward pass, again to stop scrums. The pass was settled on because Harvard Stadium had just been built and could not accommodate a wider field.
