You might already know football that’s why but it’s actually quite difficult. There are a lot of rules and you need to know the format of the field and what’s allowed and not. Positions of each player as well is a factor.
I think tennis is the easiest sport to learn
How for example running is more difficult then that?
And it doesn't really matter how easy something looks, higher the level where you are competing, learning curve will bend a lot. And you will have new standards for being good at something.
I thought acrobatics were easy as long i practiced it daily, until i met people that set my standards on whole another level. After that i realized that there was so much things i haven't learned, because i didn't knew those things were possible to learn.