During the 2012-13 season, boys’ participation in 11-player high school football declined to the lowest level since 2005-06, according to the National Federation of State High School Associations. Football, however, remained the most popular high school sport.

USA Football, an umbrella organization partially funded by the NFL, estimated the number of children ages 6 to 14 playing tackle football decreased from 3 million in 2010 to 2.8 million in 2011. The National Sporting Goods Association reported that tackle football numbers dropped 11 percent since 2011.

And participation in the country’s largest youth football organization, Pop Warner, declined 9.5 percent from 2010 to 2012, as first reported by ESPN’s “Outside the Lines.”

“There’s a natural ebb and flow in the popularity of sports but I do think that the concern about concussions, concern about the brain injuries, is also a major cause for concern in parents,” said Dr. Julian Bailes, co-director of NorthShore University HealthSystem’s Neurological Institute in Evanston, Ill., and Pop Warner’s chief medical officer.