USFL?
It was the old AFL that really shook up the sport. Before then, people really hadn't accepted the forward pass as a means of matriculating down the field.
Absolutely. Another good callout.
My example of USFL was more in regards to improving aspects of the game, yours is tectonic shifts.
FWIW, the original USFL helped influence the NFL to adopt: instant replay, two-point conversion option, 15-yard pass incidental interference, introduced the run-and-shoot style offense, and took away the stigma of touchdown celebrations. There's probably many more examples, but those are the ones I remember off the top of my head.