Year by year, seemingly, the way that the game of football looks on the field is slowly but surely being altered. The NFL looks different if you drop into any particular game than it did a decade ago, and the games from a decade ago resemble a game different from the game played a decade before, and so on and so forth.
More and more, however, the changes in the way that the game looks on the field is coming less as a result in a shifting and innovation in schematic philosophies and more as a result in the rules that govern the manner in which the game is played.