re: Mahomes is the GOAT

added notes - also stolen from reddit - pretty interesting how much the game has changed since the 70s

Ignoring some of the obvious safety-inclined rule changes (no head-slapping offensive linemen like Deacon Jones, clotheslining receivers running routes like Night Train, etc.):

For clarity, before the early 1960s most routes saw receivers and defensive backs run down the field with little to no contact but this was a stylistic choice, not one enforced by the rules. Individual players like Night Train Lane started taking advantage of the absence of rules. By the mid-60s, most coaches and defenses started taking advantage of the fact that defenders were allowed to initiate contact for the first 10 yards but receivers weren't.

1973: Defensive backs are only allowed to chuck a receiver once after they are three yards down the field.

That means a back could create contact at the line, lose that contact, and then initiate contact again as long as they were within 10 yards downfield. Obviously, this was still a significant advantage for the defense.

1974: Eligible receivers who line up outside the formation (away from the offensive line) may not be blocked below the waist at or behind the line of scrimmage

A common way to prevent a receiver from running a route was simply to cut block them. Both him and the defender covering him would end up on the ground but this obviously made him unable to receive a pass, forcing the QB to hold the ball or progress to another receiver. Plus, even if they did get up, they'd still be within 10 yards of the line of scrimmage, meaning the defender could then start jamming them.

It's important to note that even after this rule change, a cut block against a receiver was only a 5 yard penalty which meant it was still advantageous for the defense in certain situations

1978: Mel Blount Rule - no (non-incidental) contact with a receiver beyond 5 yards past the line of scrimmage.

Before this, the rule was 10 yards. Big, strong CBs could physically lock up a receiver within 10 yards before this rule

Also 1978: The rules for blocking were changed such that offensive linemen could reach out and block/grab with an open hand.

Before this, linemen were to keep their arms in a flexed position close to the chest without extending them to push. The hands had to be closed or cupped. Failure to do so would lead to either a holding penalty or illegal use of the hands penalty

These 2 rule changes in 1978 were immediately significant. In 1978, teams threw 38 percent of the time. Just 2 years later, it was up to 47%