The 1978 season was one of the most historic campaigns in NFL history. That was the year the league's rules committee made two drastic changes. These two rule changes significantly changed the game of football forever.
The first rule change was made to allow offensive linemen the now-common action of extending their arms to grab defenders while blocking. This opposed the chicken-wing style of blocking that had been allowed since the inception of the NFL. Offensive linemen used to block in a straightforward rampage leading with their helmets and nothing else but momentum to defeat an oncoming rusher. Now they could thankfully make use of their hands to block or set the run from this point.
This rule change bought offenses extra time to make plays. The league threw offenses a bone by loosening the interpretations of holding by offensive linemen. Many fans believe the league was favoring offenses, but a closer look at the defensive play of the 70s showed the league attempting to balance out the game. The game heavily leaned toward defense. Defensive lineman were borderline abusing offensive players (e.g. the no head-slapping rule.) Its more famous name, the Deacon Jones rule, was enacted in 1977 in response to defensive ends frequently slapping the helmet of opposing O-lineman's helmets. They were doing this in order to disrupt offensive linemen.
The second rule change was the shortening of the 10-yard chuck rule to five-yards. The rule is better known by its more popular title, The Mel Blount rule. While playing for the Pittsburgh Steelers, defensive back Blount was infamous for his physical play against the receivers he was tasked with covering.
Prior to the 1978 season, corners had a 10-yard grace period to make contact with receivers, the shortening of the chuck rule to only five-yards benefited receivers while being detrimental to corners.
"One of things I always wanted to do was let people know this was my territory, if you came in here, you're going to have to pay." - Mel Blount
Before this rule's inception, cornerbacks spent the better part of a decade and a half abusing receivers in what was infamously known as "the bump and run" coverage. This physical style of bumping receivers throughout their route messed up their timing with the QB and their positioning running the route. Blount at 6'3", 205 lbs was a specialist at this coverage, famously (or infamously, depending on who you ask) becoming the first cornerback to win NFL Defensive Player of the Year in 1975. He caught 11 interceptions while outright harassing receivers.
Why did the NFL enact these changes?
The league believes fans today want a 54-51 final score over a 15-12 tally. Many fans of the game recall this year as when the NFL moved to a more offensive identity, leaving it's more gritty Steel Curtain image for a more finesse-skill image best displayed by the Sam Francisco 49ers of the 1980s, whose coach Bill Walsh designed a scheme that took advantage of these two new rule changes.
Throughout the history of the NFL, the commissioner and front office of the game have strived not only to protect the sports integrity, but also have revised its playing rules to make the contests fairer, safer and more entertaining. The league must always carefully weigh all of those factors and many more before implementing any rule change.