The credits roll and the house lights come on and the old high school coach turns with his eyes as big as he can make them. Wow, he says. He thought he would hate this movie, and he had a dozen reasons ready but the one he couldn’t get past was the simplest. Just the name: “Concussion.”

“You don’t want to get me started on concussions,” Tony Severino said when I invited him.

Except I did. Actually, getting one of the longest tenured and most successful high school coaches in the city going on concussions is exactly what I wanted. Severino has been the head coach at Rockhurst High School since 1983, coaching seven state champions, an institution both at that school and in the Kansas City area.

The sport he loves is changing, and in some ways is under attack. Research and awareness surrounding head injuries is growing all the time, and has become a billion-dollar battleground in the NFL.

But the important stuff is happening at the sport’s lower levels. An NFL team is made up of 53 grown men, each paid hundreds of thousands or millions of dollars. At Rockhurst, 250 kids are out for football most years, each with developing brains and no compensation. Around the area, more than 100 high schools field football teams every year with thousands and thousands of kids.

So the important stuff isn’t necessarily how head injuries affect the professionals. It’s what happens to the kids. That’s why I wanted to watch this advanced screening of the movie — starring Will Smith, in theaters on Christmas Day — with Severino. Men like him are the ones who see the changes first, and the ones influencing the kids who will grow into the athletes we watch on Saturdays and Sundays.

I did not know what to expect and, actually, the public relations man who set up the screening was nervous when I told him who I wanted to bring. They are trying to position this as a compassionate story of the men who play football. They know some will see it as an anti-football movie, and, actually, that’s why Severino was hesitant to watch. He’s tired of defending the sport he loves.

Which is why he was surprised after watching it.

“They can call it whatever they want,” Severino said. “That’s a great movie. It’ll make our game better, and safer.”

The movie highlights the grace, beauty and power of football, but is a virtual act of war against the NFL. It’s obvious why the league has been stewing about this for months. The movie depicts the NFL going to great lengths to discredit research on head injuries, prioritizing business over safety, and shows the affects of CTE in brutal details that will be stunning to a mainstream audience.

“Concussion” portrays Roger Goodell staging dog-and-pony-show “concussion summits,” the league employing unqualified “experts,” and the doctors who discovered and promoted the findings of CTE being indicted and having to change jobs after threats for interfering with the NFL.

It is, literally from start to finish, a damning indictment of America’s most powerful and popular sports league.

Head injuries and CTE have been major topics around football for years, and new stories are told all the time uncovering heartbreaking tragedy and scary findings. But Americans are mostly visual learners, and nothing tells a story to a broad audience quite like a blockbuster movie with an A-list star and a Christmas release date.

“The awareness, I really think it’s going to help,” Severino said. “It’ll help. It’ll help coaches be more aware, it’ll help everybody. That’s the biggest thing. I just don’t want people to be afraid. There are so many great things about this game. All the things you learn about hard work, relationships, sacrifices, working as a team. Let’s get the awareness up, and it’ll come back. It’ll come back better, to be honest with you.”

Already, the game is changing at the grassroots levels. Parents are delaying when their kids start playing, or prohibiting it altogether. Youth and high school coaches talk all the time about how to navigate the change, and how to keep kids safe and parents confident. Some push to make everything below the high school level flag football.

Last season, fewer freshmen came out for football at Rockhurst than in any year since Severino’s arrival. This season, the number was even lower. The turnout for sophomores, juniors and seniors is holding steady, however, which Severino takes as a sign that the kids who never would’ve stuck with football just aren’t coming out in the first place.

There is a line in the movie where an NFL doctor says that if 10 percent of mothers perceive it as a dangerous sport, football’s profitability will end. It’s a provocative thought, and one that also appeared in League of Denial, the 2013 PBS documentary and book written by Mark Fainaru-Wada and Steve Fainaru.

You can take a lot of symbolism from that paragraph. The NFL has been motivated by self-survival instincts, and maintaining a wildly profitable business model. The implications of this issue include billions of dollars, a treasured form of entertainment, the deteriorating brains of admired athletes, and the safety of our children. It’s an enormous issue, not just in sports but beyond.

It’s also true that the movie is based on information and stories that have already been told. “Concussion” will reach a larger audience and in a more personal way than any single previous look at an important issue. But the stories have been out there for years, and well-known by parents and coaches like Severino.

So far, the changes have been mostly minor. More emphasis on tackling technique, fewer coaches running live tackling drills, and more questions from parents. The movie will raise the profile of the conversation, but any fundamental change of the sport will be based on information that so far has mostly affected only the fringes.

Those changes will take place on the watch of coaches like Severino. That’s how the future of America’s most popular sport will be shaped.

“We’re taking a hit,” he said. “But it’s such a great sport. It’ll never go away. It’s up to us to make it as great as it can be.”