Concern about the damaging effects of concussions and the efficacy of sports helmets has been growing in recent years. In 2011, the American Journal of Sports Medicine published a study that found an annual increase of 15.5 percent in concussions for high school sports over the eleven-year period from 1997–1998 to 2007–2008. For boys, football was responsible for more than half of the concussions, and for girls, it was soccer. In professional football, the National Football League (NFL) issued its first guidelines regarding concussions in 2009 and has revised those guidelines periodically—banning blindside hits to the head, imposing large fines on players responsible for helmet-to-helmet hits, mandating baseline neurological testing, and requiring players with concussion symptoms during a game to be examined by a doctor. Research indicates that although helmets reduce skull fractures and head-injury fatalities, they do not do much to prevent concussions from small as well as big hits. In 2012, former players sued the NFL for fraud and negligence, charging that the NFL downplayed the risks of multiple concussions and discredited valid research linking concussions with brain injury and dementia.