- The number of people who say they would discourage their kids from playing football has been steadily rising.

Nearly half of all Americans, according to one poll.

The worries stem from a growing body of recent research about the dangers of concussions and the drumbeat of reports about the brain damage sustained by professional football players, but, could concerns about violence ever really diminish football's hold on America?

(dramatic music) (crowd cheering) - [News Anchor] Every autumn Sunday, football's bone shattering hits unhinge NFL players across the country.

- [Narrator] Over the past several years, the National Football League has been shaken by the controversy over the long-term impact of concussions.

- In a surprise announcement, star 49er's linebacker Chris Borland says he's retiring from the NFL after just one season.

- Around training camp, there was an incident, just a mild concussion, and it, kind of, changed the way I viewed the risks of the game.

The mounting evidence and these anecdotes of guys who went through hell.

By the end of the year, I had a good idea of what I was gonna do.

For 99.9% of the people in America, football was just entertainment.

♪ Well, it Monday night, and we're ready to strike ♪ ♪ Our special forces-- ♪ - But new guys in the field are real, they're humans, and so, I think it's important to remember that.

- [Narrator] Since Borland's abrupt retirement in 2015, other players have followed suit.

But, this isn't the first time that the inherent violence of a sport has raised questions about its future.

35 years ago, it was boxing.

- In the old days, you might turn on the television, on a weekend afternoon, and three networks have a boxing match on.

In '82, particularly, there was an NFL strike and, figuring NFL fans were gonna wanna see action sports, we replaced it with boxing.

- [Announcer] Mancini is enjoying being a world champion.

- [Narrator] In 1982, Ray "Boom Boom" Mancini, the pride of Youngstown, Ohio, had won his first World Lightweight Championship.

- No, I worked so hard to get it, I'm not about to give it up now.

- Ray Mancini was a very, very popular champion.

His whole persona was of being this just, this nice kid from Ohio.

The ratings for Mancini fights were great, our highest ratings of any fighter we were doing.

- [Narrator] In November of that year, in a Las Vegas stadium, before a live CBS audience, Mancini was set to defend his title against a little known Korean challenger.

- [Ring Announcer] Fighting out of Seoul, Korea, weighing 134 and 1/4 pounds, here is Duk-Koo Kim.

- We had never heard of Duk-Koo Kim before that, but we would look at film, video tape, whatever we could get of him fighting, and we knew he was a very tough guy.

We didn't want a guy who was gonna run.

We wanted somebody who would stand there and exchange, and that was Kim's style.

(dramatic music) (bell rings) - [Sports Announcer] And there's the bell, we are underway-- - Kim built a coffin and he put it next to his bed, and he told his people, "Either Mancini's coming home in "that, or I'm going home in that."

Put on a lampshade, "Kill or be killed."

To him, it was a live or die situation.

- It was a brutal fight, in fact, Kim was the aggressor more than Ray, for the most of the fight, but there was never a point where you thought one guy was beating the other guy to the point where a referee should have stopped it.

- [Sports Announcer] Duk-Koo Kim.

You may not have heard of him before, but you will remember him today.

Win or lose.

- I was hitting him with shots, but he was still moving, making me miss too.

He still had the wherewithal to move his body, bob and weave.

You can't stop a fight when the guy has the wherewithal to do that.

- [Sports Announcer] Champion of the world, and there is 21 year old champion Ray "Boom Boom" Mancini.

- It was a great punch, and with a right shot, he went down, we just jumped.

It was glorious, because it was a great win.

Nobody knows what was going into, nobody knew.

- I planned on a long fight, everybody didn't know about that.

I saw films, the guy was very, very impressive, tough, rough, hungry, determined.

Those are the worst kind.

- The next morning, I called and said, what's going on?

And he was still in the hospital, and in bad shape, and then it was pretty much, we all knew what was gonna happen.

You know, he wasn't coming out of this.

- I was stunned, I was like, in a dream world, you know, from the highest of the highs to hit the lowest of the lows.

- A professional boxer lies near death tonight.

He is Duk-Koo Kim, a 23 year old, South Korean lightweight.

- The boxer's mother pleading with him to, "Please wake up," and, "Open eyes," before she was led from the room weeping.

- When you fight fighters from another country, they're fighting for more than themselves, they're fighting for their whole country.

They carry their dreams and hopes of their countrymen on their backs, (exhales) that's a load to fight, that's a hard load to fight.

- [Narrator] Kim's death was far from boxing's first black eye.

In the early 60's, fighters Benny Paret and Davey Moore died in back-to-back years, after major fights broadcast across the country.

- [TV Announcer] To the canvas, and look at him there.

- At that point, there was a sense of, wow, is boxing really even a sport.

In the mid-seventies you have the sense of impropriety that has been an aspect of boxing's DNA for many decades.

And then, in '82, you had Ray Mancini and Duk-Koo Kim.

- And then two weeks later, I'm watching the news' fight with Randall "Tex" Cobb and Larry Holmes.

(crowd cheering) - [Sports Announcer] It's just terrible.

I wonder if that referee understands that he is constructing an advertisement for the abolition of the very sport that he's a part of.

- Cobb was a punching bag, I mean, his head was bobbing back and forth, on and on and on.

- [Sports Announcer] From the point of view of boxing, which is under fire, and deservedly so, this fight could not have come at a worse time.

- And I just said to myself, "This is crazy.

"How can I, as a physician, possibly admire this, "enhance it, support it, and not work against it."

- Boxing attracts big television audiences.

It has drawn the attention of writers from Virgil to Hemingway to Norman Mailer, but today, the American Medical Association came out swinging against the sport.

- [Reporter] The AMA journal says that, "boxing is "an obscenity that should not be sanctioned "by any civilized society."

- The purpose of the boxing match is for one person to injure his or her opponent.

Now, when one knocks somebody out, one damages the brain, one tears brain cells.

- I don't think fight fans said, "Okay, that's it, "I'm never gonna watch another fight," just as they didn't say, "Okay, I'm never gonna smoke another cigarette," when they put a warning on the pack.

But, sponsors started to pull back and say, "You know, you're asking us for a lot of money, "you networks, to pay for your exorbitant rights fees "on football, and basketball, and baseball, "and with all the bad publicity boxing is getting, "you know what, we just as soon not do it."

- Before the Kim fight, I was being offered all kind of endorsement deals.

After that, everything went away, man, it just vanished.

I understand that now, I understand now, but, at the time, I was a kid, I was heartbroken, I didn't know why, you know.

It just all went away.

- [Narrator] For decades, stories of young boxers from blue collar backgrounds fighting their way to fortune had captivated the public, both in real life-- - I do it because I'll leave, I'll leave the ghettos.

- [Narrator] And on the big screen.

♪ Trying hard now.

♪ - The American Medical Association-- - [Narrator] But before long, the medical community began to make in-roads in their fight against the sport.

- The American Academy of Pediatrics came out with a formal position that children shouldn't box.

I took a position that, for any parent who put their child into a boxing situation, that should be considered child abuse.

- [Narrator] And on television, beer companies were soon one of the only marquee advertisers still associated with boxing.

- [TV Announcer] WBC Heavyweight Champion Fight is being brought to you by Budweiser.

For all you do, this Bud's for you.

- Sponsors withdraw so network TV doesn't want to broadcast it, so people don't see as much boxing, so they don't know as much about it, so sporting media doesn't write about it as much because they say people don't watch boxing, they're not interested in it.

And, because media isn't reporting on it, people learning about it even less, and it becomes this feedback thing, and before you know it, suddenly, it's a niche sport.

- [TV Announcer] The legendary Julio Cesar Chavez returns to the ring Saturday, October 12th on pay-per-view.

- There's something fundamental and primal about boxing.

But, as society shifts, there are legitimate questions of, "Well, do we still want to do this?"

It's that drip, drip, drip.

That constant sense that that is what boxing is about.

If that becomes a prevailing feeling about football, then the discussion changes.

- Look at this point, we know how dangerous football is.

Anyone who continues to believe that professional football players aren't, potentially, shortening their life span by playing this game is, sort of, living on another planet.

- [News Anchor] More players are suing the NFL, claiming the league failed to properly protect them from concussions and brain injuries during their careers.

- [Narrator] Faced with medical evidence about the health risks posed by the game, the NFL has started making payments to retired players who have suffered brain trauma.

Payments that could total as much as one billion dollars.

- [ TV Announcer] If there's a way to do it better-- - [Narrator] The league has also promoted its efforts at making the game safer.

- [Man] Changes were made to the kick=off this year, important changes.

- [Narrator] All aimed at addressing the criticism of a sport with more money and power than any in American history.

- You now make about 10 billion dollars a year in gross revenue.

You said that by 2027, you would like to see 25 billion.

- We don't want to become complacent.

- The NFL has a big issue in the concussion, the head injury situation, huge issue.

But, there is an entity called The National Football League.

There's a controlling entity, there's a managing entity.

Football has the NFL to solve its problems or, to at least, to attempt to solve its problems, that has a PR machine to tell the public that, "We're working on this."

Boxing was controlled by promoters and the networks back in the day.

So there was no such thing as boxing, it had no ability to defend itself because there's no organization and that might have been one of the biggest problems they had.

- [Narrator] The future of football is playing out on local fields around the country where flag football is gaining popularity after news stories about concussions in high school players.

- There is a certainly a double standard when, if you support football in the sense that you watch it and then turn around and don't allow your child to play it, the question is kind of like about by watching it, are you necessarily condoning it?

It's so ingrained in our culture that it does take a kind of real active protest and resistance to turn away from it.

- [Narrator] Over three decades have passed since the Kim/Mancini fight stoked medical concerns about boxing.

Then, in one week in July 2019.

- Max, I'm gonna stop it.

- For what?

- Max, you're getting hit too much.

- [Narrator] Two boxers died from injuries suffered in the ring, but, compared to the swiftness with which boxing was relegated to the sidelines of American life, football still holds its appeal.

- If somebody were to die during an NFL game, being broadcast live, the massive social media response, would that cause a greater, perhaps long term response?

Or would it mean that everyone went through their cycle of grief and outrage in a couple of days until Kim Kardashian did something else?

I don't know.

I'm very curious to see what happens in society over the next decade or two.