Short answers, pulled from the story.
The first American football game was played on the 6th of November 1869, between the college teams of Rutgers and Princeton. Each side had 25 players and used a round ball, and Rutgers won 6-4.
Walter Camp, a Yale player, is regarded as the Father of American Football. In 1880 he secured rule changes that reduced teams from fifteen to eleven players and introduced the snap, and in 1882 he created the system of downs.
The system of downs was introduced after the snap allowed teams to hold the ball indefinitely, producing a 0-0 block game between Yale and Princeton in 1881. Walter Camp proposed a rule in 1882 limiting each team to three downs to advance five yards, which made American football a separate sport from rugby.
The American Football League launched in 1960 to compete with the NFL and merged with it fully in 1970. The merger created a common draft and an annual championship game between the two leagues, which became the Super Bowl, first played at the end of the 1966 season.
A touchdown is worth six points, a field goal three points, and a safety two points. After a touchdown a team attempts a try worth one point by kick or two points by a conversion play, and a safety is the least common method of scoring.
Repeated concussions and sub-concussive head impacts can increase later-life risk for chronic traumatic encephalopathy, dementia, Parkinson's disease, and depression. A 2018 study found that playing tackle football before age 12 correlated with earlier onset of CTE symptoms by an average of two and a half years per year played.
Flag football, a non-contact variant of American football, will debut as an Olympic sport for men and women at the 2028 Summer Olympics. The standard form is not an Olympic sport but was a demonstration sport at the 1932 Summer Olympics.