'football is THE most demanding physical, mental, and strategical game on the earth.'
Physical.
Im sorry, but how many yards do you run before play stops? Like..5? You rest for 30 seconds... then sprint another 5 yards.
Soccer (which, incidently, is the original 'football'... as you use your foot, on a ball.) players run something like 10 miles in a game, and most of that is sprinting, with very little rest.
Rugby players run a similer distance, but they have the tackling and body contact of american football involved as well. Without the big ass mofo pads. I won't get involved with things like triathalons, and endurance events..they just speak for themselves as far as physical exertion goes.
Mental.
While it does have it's merits, there are plenty of sports which have equivalant mental aspects to it.
Tactical.
Again, many sports have equivalant or better tactical aspects to them. Take chess for example.
While it can be a hard game, I think you'll be hard pressed to claim it as the most physical, mental and strategical game, in the world...
What gravity?