On a cool August morning in Napa, the Oakland Raiders and Detroit Lions gathered on the grassy fields behind Redwood Middle School for a joint training camp practice.

About the series
For years, mounting evidence has linked football violence with brain trauma and life-threatening conditions. Now that we know the sport can produce deadly results, where do we go from here? The Chronicle offers this special report on The Future of Football.

After a long offseason, the sound of cracking pads and quarterback cadence signaled the return of NFL football. Eager spectators filled metal bleachers overlooking the action, welcoming the early signs of the coming season. The crowd included players from a pair of local high school teams.

Following the practice, Raiders head coach Jon Gruden was asked about having those young athletes in attendance. What did it mean to him? Why bring them out? His answer was emphatic.

“I think it’s smart for everybody at this level, pro football, NFL, to give back to youth football,” Gruden said. “We’ve got a problem, I think, in this country. The game is under siege by a lot of people who don’t think it’s a safe game. They don’t think it’s a good game anymore. And I think that’s hogwash.”

Five-year-old Rashawn Munmon of Berkeley Jr. Bears Pop Warner Football gets help with his helmet in San Jose on Aug. 26.

(Scott Strazzante / The Chronicle | San Francisco Chronicle)

Gruden’s passion speaks to the growing debate surrounding youth football. Many love the sport. But mounting evidence shows that playing football can be extremely dangerous, even deadly in the long run. Is it a good idea for young players to participate? That is an increasingly louder discussion.

By almost any measure, football remains the most popular sport in the United States, a fact reflected by the number of those who play it. According to the National Federation of State High School Associations (NFHS), more than 1 million boys played football nationally in 2017 — nearly equaling the totals of basketball and baseball combined. Thousands more suited up for youth leagues like Pop Warner, beginning as early as age 5.

Yet those numbers are decreasing. The number of high school boys playing tackle football has been in slow but steady decline for nearly a decade. The trend has coincided with heightened concern about the frequency and lasting impact of head injuries on young athletes — with former NFL stars among those questioning whether they’d let their sons play football, and some states weighing whether to establish minimum age limits for the sport.

A recent Friday night in the Bay Area provided a jarring snapshot of football’s risks. On Sept. 21, Heritage-Brentwood and Freedom-Oakley each had a player airlifted to a local hospital after sustaining in-game injuries. Another game between Benicia and St. Patrick-St. Vincent-Vallejo was reportedly cut short after several SPSV players exited with injuries. The injured players from Heritage and Freedom were both released from the hospital shortly thereafter, according to team and school officials.

Such incidents have led some parents and players to consider other options.

Overall, participation in 11-player football fell about 6.9 percent between the 2008 and 2017 seasons, according to the NFHS.

The trend has led Roger Pielke Jr., director of the Sports Governance Center at University of Colorado, to study the numbers and draw a conclusion.

“There’s enough evidence to say that football, as a youth sport, has peaked,” Pielke said.