Before the 1978 season, the NFL's owners passed a shit-ton of rules that were designed to scale back the role of physical contact in the game. Under the new rules packages, wide receivers could not be bumped more than five yards from the line of scrimmage. Offensive lineman were allowed to use your hands. Even changes to the field were made, the hashmarks were brought closer to the middle of the field. In the evolution of the professional game, these 1978 changes are widely considered to have had the greatest impact on the game.
The rulebook today gets minor edits by comparison, and the more notable changes have less to do with the play of the game and more to do with protecting the multi-million-dollar assets on the field. The most obvious of these is the crackdown on quarterback hits; too far down, in this asshole's opinion. Whether they be late, below the knee, between the earholes, or while the defender holds a piece of non-kosher meat, these hits are being called as penalties more often than not. "Horse-collar" tackles and hits below the knee also are now being penalized, in light of prominent players (and in some cases, their teams) having their seasons and ligaments ripped out from under them after being injured as a result of these techniques.
These extra rules are just one concession that teams are forced to make, based on player supply. Many followers of the game have argued that, with 32 teams consisting of 53 players per roster, there aren't enough good players to go around. This does not seem to stop teams from releasing the average player after less than four years of service, but never mind that for now. With players more expensive, their health remains critical to the bottom line. The violence that has been a staple of this sport for so long, that has led to players being spit out by this league, time and again, may itself be on the downside of its usefulness.
Fortunately, this league, this game, has collisions and unpleasantness to spare; smashing your body into that of another person at a high, heterosexual speed remains a staple of football, and it always will. The real danger is where the judicious forces could take control of the league yet again, and warp it into something deemed better for the sake of competition, only to dissolve the game's essence even further. That shouldn't be an issue today, where the league will finally do what it does best: get the hell out of the way while millions of people watch grown men beat the shit out of each other.