Rules to keep in mind when comparing players

[RyanChristiansen]

What rules changes do you feel changed the game so signficantly that it's not fair to make comparisons between players before and after the rule went into effect?

For example, in 1978, the NFL ruled that a defender would only be allowed to maintain contact with a receiver within five yards of the line of scrimmage. Is it fair to compare receivers who played their entire careers before 1977 with receivers who played 1978 and later? What about receivers who straddled the rules change?

For example, from 1975 to 1977, there were 13 receivers in the NFL who had 100 or more catches and averaged 15 or more yards per reception. From 1978 to 1980, there were 27 receivers in the NFL who had 100 or more catches and averaged 15 or more yards per reception. Clearly the rule affected production.

Also, in 1980, the NFL ruled that players were not longer allowed to strike, swing, or club the head, neck of face, or the result would be a personal foul. This changed the game significantly for guys on defense and made it easier for offensive linemen to pass-block. Is it fair to compare defensive linemen who played their entire careers before 1980 with d-linemen who played 1980 and later? What about d-linemen who straddled the rules change?

From 1977 to 1979, there were 57 defensive linemen who had 15 or more sacks during that span. From 1980 to 1982, there were 41 defensive linemen who had 15 or more sacks during that time span.

From 1977 to 1979, there were 105 defensive linemen who had 9 or more sacks during that time span. From 1980 to 1982, there were 86 defensive linemen who had 9 or more sacks during that time span.

Keep in mind that while Pro Football Reference now estimates it has 99 percent of the sacks from the 1970 AFL-NFL merger through the 1981 season accounted for, as well as about 95 percent of sacks in both the AFL and NFL from 1966 to 1969, and about 80 percent of sacks from 1961 to 1965, those sack statistics are unofficial. Only sacks from 1982 and later are official.

And what about quarterbacks and receivers on either side or who straddled that divide?

[ChrisBabcock]

When the intentional grounding rules were changed (2010 or so), QB interception totals dropped significantly. In the past, even outside of the tackles, a passer had to have a receiver in the vicinity when throwing the ball away. This would add to INT totals on plays like that. Now a QB can just chuck it into the stands.

[JeffreyMiller]

Not rule changes but significant shifts in style ...

Teams moving from the single wing to the modern T

Teams moving away from 60-minute men to two platoon

[RyanChristiansen]

Also, the war-affected seasons, 1942-1945. Accomplishments during those years were amongst the best available, not the best possible. How to think about those years is tricky.