The FIFA World Cup is underway and millions of people around the globe are watching the most popular sport in the world. In fact no other sport even comes close to matching the appeal of football. But why do so many people like to play it and watch it? It is unlikely that this is arbitrary, and there has to be some specific set of characteristics that makes football so appealing. Here, I suggest some reasons why football has such mass appeal. Some points may seem obvious, but are worth addressing anyway.
First, perhaps the evolutionary history of Man plays a part. Historically men have hunted and fought in groups. The need to be part of a team to achieve some goal may still be ingrained in us. Since hunting or going to war for fun is going to be met with harsh criticism, we make do with team sports instead where football fits in perfectly.  Something like cricket could also be called a team sport, but each player functions more individually. In football players are dependent on each other and teamwork is crucial, and perhaps that appeals more to our evolutionary leftovers.
Football is also a very easy sport to play and to follow. Though the talk of double pivots and false nines can make football seem complicated, fundamentally it’s just two teams trying to kick a ball into a goal. There’s only one way of scoring and no restrictions on where you can score from. Even if one has no idea how it works, a couple minutes watching a game is all one needs to learn about it.
You don’t need any preparation or equipment to play, except a ball and a goal post, which could just a couple of sandals on the floor or a chalk outline on a wall. You could play in your living room (and break your mother’s favourite possessions) or you could play on a field. Two people can play it, or twenty-two, which is about the most number of people you could get together for a game anyway.

World class players in football come in every shape and size.

Moreover, unlike many sports, football does not bias against any type of physique. If you weren’t at least 7 foot tall in basketball or a muscle-bound giant in rugby, you’d be at a massive disadvantage. In football there is a role for any type of physique. World class players in football come in every shape and size, from the miniscule Messi to the rampaging Yaya Toure, covering much of the distribution for adult height and weight. Almost anyone could be really good at football and enjoy it.
Finally, football is a very exciting sport and is so in a number of ways. There is only one break in an official game (that does not go into extra time), the action never stops, there are no intrusive TV adverts unlike many sports (for example, cricket and, for a loose definition of ‘sport’, American Football), and it’s a low scoring game. The last point may seem contradictory. Goals are exciting, so shouldn’t a sport where a lot of goals are scored be the most exciting?

Well, think about basketball: an official game lasts 40 minutes or so, but each team can score over 70 points. Even if we assume all points scored were three pointers, that’s more than 20 goal scoring events per team. Where goals are so common, there’s little tension; it doesn’t matter much if your team scores and gets ahead, because it’s very likely the other team will score too, and vice versa. And if there are a lot of goals, the value of each goal is decreased. When a player scores it’s not a huge achievement. And when a lead is large enough to matter, or a player has scored a significant amount of times, it has happened over so many little steps that the euphoria is diluted.

Worst game of FIFA ever.

Goals in football are rare and so each goal means a lot. When you or your teammate scores, even just once, that could be the winning goal, so all the joy and triumph is delivered in one moment and feels stronger. Because of the low scoring nature of the game, there is also a lot more tension, which means better entertainment. Even a cagy game that ends 0-0 could be entertaining. Imagine the score being 0-0 at half time, one goal could likely win the game for either team; it’s this tension and anticipation that makes football so entertaining.
Football’s popularity isn’t due to chance, but stems from a unique set of characteristics. These characteristics appeal to human nature and make the sport very widely accessible, and, importantly, do so without any cost to entertainment, and hence have ensured football’s place as the most popular sport in the world.