High school football participation may have peaked.

That’s the argument I make in a recent analysis for the international sports governance association Play the Game.

The conclusion is based on data indicating that after decades of continuous growth, high school football participation numbers peaked in 2009 when looking at the total number of players, and in 2013 if you looked at participation as a percentage of eligible boys.

The article led to many reactions. I heard from coaches and parents who explained that the national data jibe with their local experiences of declining participation. I also heard from a lot of people who were interested in the very public spat between the NFL and President Trump, and how this might influence future participation rates. (Their concern was that some parents may keep their kids out of football if the sport becomes too politicized.)

The article also prompted some questions. Is the decline real? What does it mean for the future? And how does football compare to participation in other sports?

The decline in football participation is real. I spoke with Chris Boone, assistant director of publications and communications at the National Federation of State High School Associations, about their fantastic data set, which has tracked high school sports participation for almost 50 years. Boone told me that the NFHS data set is the “best instrument there is” on participation, and “98 percent of U.S. high schools” are included in their annual surveys. The NFSH tracks more than 70 sports for each boys and girls. The data look to be the best tool we have to track long-term trends in participation rates in U.S. high school sports.

As I explained, the decline in participation in football is relatively small – a decline of just of 50,000 players over seven years, from a base of 1.14 million in 2009. But, based on the coverage and quality of the data set, it also does appear to be real and not a statistical or methodological quirk.

No one knows how future participation will evolve. The recent inflection point – several decades of steady increases in football participation followed by several years of decline – could signal a long-term change or simply represent a short-term aberration.

What’s clear is that there are numerous factors in play that suggest that the short-term trend may continue for a while. Most notably, there is mounting evidence of growing parental concerns over health risks. Changes to the game that enhance player safety, medical research that more precisely identifies the causal pathways leading to long-term health effects and even presidential politics all might play a role in the future popularity of football.

But make no mistake, football remains extremely popular.

To place these trends in a broader context, I’ve taken a deeper dive into the NFHS database for both boys’ and girls’ participation in high school sports.

Football is, by an overwhelming margin, the most popular high school sport for boys. Over 400,000 more boys played football than track and field, the second most popular sport.

Whatever the future of football, total participation numbers suggest that it’s likely going to be years before football is dethroned as the “king of sports” among boys.

Yet participation rates continue to evolve in these seven boys’ sports, and the numbers show that football isn’t the only sport that has seen as recent decline; wrestling has, too.

The biggest increases for boys have been in cross country (45 percent), soccer (37 percent) and outdoor track and field (25 percent). The smallest increase since 2000 is in basketball (2 percent), which has seen fairly constant participation rates.

As with boys, the sports seeing the greatest increases in participation for girls are cross country (46 percent) and soccer (43 percent).

The success and popularity of the 1999 Women’s World Cup-winning team no doubt played a role in the sport’s explosive popularity at the turn of the century. If recent rates are any indication, it won’t take long for soccer to surpass volleyball, basketball and even outdoor track and field. (We’ll have to wait and see if the U.S. men’s national team’s failure to make the 2018 World Cup has any detectable impact on participation.)

But if sport is a reflection of broader society, these numbers could be a response to the forces of globalization: Around the world, soccer and track have a much high prominence than they have historically had in the U.S. The globalization of international soccer, which includes soccer’s growing presence on U.S. television, would suggest that this trend might continue.

Of course, traditional American sports – football, baseball, softball, basketball – still dominate. Their growth has simply slowed since 2000.

But football’s recent decline – however slight – suggests that something’s at play at the grassroots of America’s most popular sport. Data are not destiny, but football lovers across the country should consider this evidence an early warning that all is not well in the sport.

Roger Pielke, Jr. is the Director of the Sports Governance Center at the University of Colorado Boulder. He also serves as co-president of the board of directors of FC Boulder, a youth soccer club.