I've played all of these sports (except basketball) and I do feel that they are much more difficult to play than football
Are we talking about just
playing it? Or playing it competetively?
Football is easy as hell to play, and requires no skill apart from being able to walk -- although you don't really have to do that.
However, If you want to play it competetively, then it is one of the hardest. You have to be strong, agile, skillful, intelligent, fit, confident, and co-ordianted. All of these are incredibly important in the game.
In American Football for instace, all you need to be able to do is Run into people, and do what you're told by the coach. There are a few players who will run around and throw the egg, but largely, they do nothing.
Besides that, they stop playing every 10 - 30 seconds, and have a wee break and talk about what they are going to do next.
Baseball, all you do is swing your arm and then run. This only requires hand-eye co-ordination, and maybe a bit of speed. Power isn't that important if you get a good connection.
Besides that, after they've hit it, they either just stand around, or sit around. Not demanding.
Basketball is in all fairness quite demanding. And i've not got too many issues with it being higher than football, it should be about equal. The same goes for Ice-Hockey, although maybe less so.
Tennis?

I am a keen player, and there is no chance in hell that it is more demanding/harder than Football. Just no.
It is a biased poll, and its not really something you can measure anyways. Difficulty of sport varies depending on your defenition of difficulty, and your experience playing the sport.