What is the significance of the 20 yard line?

Question

I can think of two instances where this comes into play. One is if the kick-off falls behind the receiving goal line, and the runner chooses to "down" the ball in the endzone rather than run it out. This allows the receiving team to start at 20 yard line "for sure" instead of taking their chances with a running play.

The second is if the offensive team's ball carrier is tackled in his own end zone for a "safety," this team has to make a free kick from its 20 yard line (instead of from the 40 yard line).

How and why was the 20 yard line chosen for these purposes? And why was the "20" yard line changed to the 25 yard line for both touchbacks and safeties in college football in 2012?

Answer 1

Also add to this an offensive player fumbling into the endzone and recovered or out of bounds, an interception in the end zone kneeled, and a couple of blocked kick rules (and I fear I am missing things).

As far as I know, the touchback was an original (or very very old rule). I have a pretty good idea of the history of most rules and the 20 yard line for touchbacks or change of possession rules has not been changed or altered for quite possibly the past 100 years.

What is the significance? It is just the "average" spot that worked out as a good starting spot. If an offense started out at the 10 yard line then a penalty and a sack results in a defensive advantage (hardly ever has a team started out on their 20 or greater and got a safety). If an offense started on the 30 they would need just 30 more yards and most NFL kickers would be in range.

The significance of the 20 yard line is that it was such a well picked spot on the field that the original rule makers were exactly right. If the 20 spot had problems rule changes would happen. Only in 2012 did college change touchbacks to the 25. And that had nothing to do with creating a fairer/better governed game. It was just so that they could convince college coaches to have their guys take a knee so that the 22 guys on the field, probably never seeing the pros didn't get hurt.

Answer 2

Another significance of the 20 is that when an offense advances the ball to within 20 yards of scoring a Touchdown, they are considered in the "red zone" for statistical purposes.

As the Coach said in his answer, the 20 was an average spot a return man could get to if he ran out a kick off out of his end zone. Additionally, the touch back rule is important because it forces kickers to strategical kick the ball rather than always kicking it beyond the end zone for a automatic touch back.

As for college, I'd like to expand on that answer. With the prevalence of new concussion research and repetitive head trauma, it was determined that kick offs have the highest likelihood of high impact concussion inducing plays. By awarding 5 extra yards to the touch back rule, the receiving team is encouraged to take a touch back so as to prevent as many high impact head blows as possible.