Actually, I CAN answer that. Football is a collective term for all forms of sport played "on foot" (by the working class) as opposed to "on horseback" (by the upper class). There are many types of football all around the world including association football (soccer -- the word coined by the English), rugby football, Australian rules football, and gridiron football (American). In America, there is no need to qualify gridiron football since it is the predominant sport and the word "soccer" is available -- just as the English do not qualify association football versus rugby football. They are simply football and rugby.
Football -- played "on" foot / not "with" the feet.
You were saying something about not knowing your ass from your elbow...