<P> Football is a full - contact sport, and injuries are relatively common . Most injuries occur during training sessions, particularly ones that involve contact between players . To try to prevent injuries, players are required to wear a set of equipment . At a minimum players must wear a football helmet and a set of shoulder pads, but individual leagues may require additional padding such as thigh pads and guards, knee pads, chest protectors, and mouthguards . Most injuries occur in the lower extremities, particularly in the knee, but a significant number also affect the upper extremities . The most common types of injuries are strains, sprains, bruises, fractures, dislocations, and concussions . </P> <P> Repeated concussions (and possibly sub-concussive head impacts) can increase a person's risk in later life for CTE (chronic traumatic encephalopathy) and mental health issues such as dementia, Parkinson's disease, and depression . Concussions are often caused by helmet - to - helmet or upper - body contact between opposing players, although helmets have prevented more serious injuries such as skull fractures . Various programs are aiming to reduce concussions by reducing the frequency of helmet - to - helmet hits; USA Football's "Heads Up Football" program is aiming to reduce concussions in youth football by teaching coaches and players about the signs of a concussion, the proper way to wear football equipment and ensure it fits, and proper tackling methods that avoid helmet - to - helmet contact . However, a study in the Orthopaedic Journal of Sports Medicine found that Heads Up Football was ineffective; the same study noted that more extensive reforms implemented by Pop Warner Little Scholars and its member teams were effective in significantly reducing concussion rates . </P> <P> A 2018 study performed by the VA Boston Healthcare System and Boston University's school of medicine found that tackle football before age 12 was correlated with earlier onset of symptoms of CTE, but not with symptom severity . More specifically, each year a player played tackle football under age 12 predicted earlier onset of cognitive, behavioral, and mood problems by an average of two and a half years . </P> <P> The National Football League (NFL) and the National Collegiate Athletic Association (NCAA) are the most popular football leagues in the United States . The National Football League was founded in 1920 and has since become the largest and most popular sport in the United States . The NFL has the highest average attendance of any sporting league in the world, with an average attendance of 66,960 during the 2011 NFL Season . The NFL championship game is called the Super Bowl, and is among the biggest events in club sports worldwide . It is played between the champions of the National Football Conference (NFC) and the American Football Conference (AFC), and its winner is awarded the Vince Lombardi Trophy . </P>

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