AMNA NAWAZ: Fans and families will pack the bleachers tonight in high school stadiums across the country as football season kicks off in earnest.

But after at least seven deaths tied to the sport since August, including three teenagers who sustained fatal brain injuries, questions are being raised again about the safety of the game played under those Friday night lights.

William Brangham has more.

WILLIAM BRANGHAM: One of those deaths was a boy named Cohen Craddock, a 13-year-old from West Virginia who suffered a head injury after making a tackle in practice.

His father is now advocating for the use of padded helmet coverings known as guardian caps, and he wants his son's teammates to stick with the game.

RYAN CRADDOCK, Father: I told them that this is about that this was a bad accident, to move forward.

I didn't want them to have the weight of my son on their shoulders.

But I wanted them to play for him.

I wanted them to play Cohen-strong.

I don't think we need to take away football.

I just think we need to maybe put more safety measures out there to protect our kids.

WILLIAM BRANGHAM: For more on the risks and rewards of youth tackle football, we're joined by Chris Nowinski.

He's the co-founder of the Concussion Legacy Foundation, a neuroscientist and a former college football player himself.

Chris Nowinski, welcome to the "News Hour."

We just heard from that father, Ryan Craddock, who tragically lost his son to a traumatic brain injury in football.

Help us understand these numbers in perspective.

Why is it that it seems that tackle football exerts such a heavy toll?

CHRIS NOWINSKI, Co-Founder and CEO, Concussion Legacy Foundation: Well, I'm going to focus on the traumatic brain injuries.

And I don't think, unfortunately, we can be that surprised that a few kids die every year playing football.

There will be a billion head impacts created by the game of football this fall.

So it's almost a miracle that there's only a few deaths.

And that's because helmets have actually done a good job of preventing deaths, but they don't prevent every possible brain injury.

The other thing to talk about is, what are those billion head impacts going to do over time?

And so we will lose a couple now, every year, and then -- but more will suffer long-term effects down the road.

WILLIAM BRANGHAM: So is that just the science indicates that repeated percussion, if it's not a traumatic event in the moment that results in these tragedies we're talking about, but that repeated percussion to the brain over time has real problems as well?

CHRIS NOWINSKI: Right.

And that's the area of research that I have focused on for the last 20 years, is that having played -- I took 10,000 head impacts.

I survived, like most people do.

But I didn't realize until after I stopped playing that had laid the groundwork for the potential for me to have a disease called chronic traumatic encephalopathy.

And I think that's where we really should be focused on.

These unfortunate deaths give us a window with the fact that our brains are very vulnerable.

And those hits add up over time.

And what we're finding is that, if you have a long football career, and you take hundreds or thousands of head impacts, the longer you play, the greater your odds you will develop a degenerative brain disease that will change who you are.

And to be honest with you, like, I started this so long ago, but I have recently lost friends.

I lost one of my teammates at Harvard to this.

So it's just -- it's a serious issue.

WILLIAM BRANGHAM: And what do you say to the many parents who say, I hear about those risks, those are isolated, perhaps tragedies, but there is so much upside to this?

There's sportsmanship.

There's camaraderie.

There's great exercise, the spirit that this brings to young athletes.

How do you help parents weigh the benefits with these risks?

CHRIS NOWINSKI: Children, unfortunately, will die in these activities.

Some have died randomly from heart disorders and other things.

So the deaths don't really tell us what to do.

The way I advise parents on youth sports is, we absolutely want our kids playing sports and team sports.

They do wonderful things for their physical and neurological and mental development.

But what we don't need and what we have, what we should get rid of is our children getting hit and head hundreds of times a year.

Not every sport has that.

Only a few have that.

And those that do introduce a risk of concussions that can change kids and this risk of CTE.

So, yes to sports, but say no to the head impacts.

If your kids take in more than 100 head impacts every fall in this sport, maybe try another sport, at least until their brain has had time to develop and grow.

I would consider maybe 14 to be a good guideline.

No head impacts repetitively before 14.

Let their brain grow, and then you can take greater risks, when the kids might understand what they're getting into.

WILLIAM BRANGHAM: What else practically can parents do?

We heard from that father, Ryan Craddock, saying that he wants kids to wear these pads on their helmets.

Is there any evidence that any type of additional protection can protect the head during tackle football?

CHRIS NOWINSKI: Better helmets are a little better protecting against concussions and brain injury.

There's mixed evidence on the additional pardons on the outside.

What I would recommend parents do before they get into equipment is have a conversation with their child's football coach about how they practice.

The conversation that we're not having at any level outside of the NFL is, we can change practice and get rid of probably half the head impacts, half the risk if we just make a commitment to teaching kids how to play football successfully without them getting hit in the head every day.

And the NFL has almost eliminated hitting from practice, but that's because the players fought for it.

And 12-year-olds can't get together and stand up to their coach and say, hey, why aren't we practicing with our helmets and shoulder pads?

Why don't we learn this game another way?

But that is the -- by far the number one thing that we can do to make football safer, change practice.

WILLIAM BRANGHAM: All right, Chris Nowinski of the Concussion Legacy Foundation, thank you so much for being here.

CHRIS NOWINSKI: Thank you.