Contents [hide]
1 Etymology and names
2 History
2.1 Early history
2.2 Evolution of the game
2.3 The professional era
3 Teams and positions
3.1 Offensive unit
3.2 Defensive unit
3.3 Special teams unit
4 Rules
4.1 Scoring
4.2 Field and equipment
4.3 Duration and time stoppages
4.4 Advancing the ball and downs
4.5 Kicking
4.6 Officials and fouls
5 Safety
6 Leagues and tournaments
6.1 Rival professional leagues
6.2 International play
7 Popularity and cultural impact
8 Variations and related sports
9 See also
10 Footnotes
11 References
12 External links