There was a caveman who just came back from skinning and gutting a pig. Then the man with the skin and the guts of the pig, put the guts into the skin and made it into a ball. And then decided to through the ball of guts at his friend, and then his friend threw it back at him. And they did this for days on end, and had a lot of fun.
Then the caveman decided to add more people to this game of catch, and they all played catch everyday. And after some time they all grew board of catch, so they all wanted to hit each other, and so now they are hitting the perosn with the ball
As the thing that these cavemen created was past down from generation to generation the activity started to build in major popularity. And has the game became more apparent it started to have more rules, such as gear for the people involved in order to prevent the frequent injuries that came before. There was also another rule added to the early evolution of this sport, there was the rule of the limit in space which you have, in order to prevent long drawn out games. Which helped this sport grow in popularity.
Then the sport started to quickly become very popular across the world. The sport really started to be enjoyed by many people in the US, that the United States turned it into a nationally televised event. Then to ensure more players will participate in the games they added more rules to the game, to make for players to not get so injured so frequently and so that the league can make more money... I mean more enjoyment for the people who watch.
Before the more adavnced gear
Then the sport found a universally loved name. The name that was chosen was Football and the sport has been participated in since the early 1800's. And now the sport makes billions every year, and still continue to grow in popularity every year.