http://i.imgur.com/Y6Nve01.jpg
At point "A" you can see the current Stanford Linear Accelerator complex for comparison. At 2 miles (3.2 km) in length, SLAC is currently the longest linear accelerator in the world. The ILC would be nearly 10 times the length.
For further comparison, the main accelerator ring at CERN is 27 km in circumference, and the arms of LIGO are each 4 km in length.
There'll probably soon be confused replies to this comment from Europeans: "But that is a football field!"
As to why we have two games,
(a) A game where you occasionally kick the ball, but mostly you toss the ball and carry it around,
(b) A game where you occasionally hit the ball with your head, knee or chest, but mostly kick the ball around, and touching the ball with your hands is not allowed,
Why (a) is called "football," and (b) is not, I don't know. Historical accident, maybe?
Sports is definitely not my strong point. I would probably have been better at gym class if it'd been about things like the etymology of the word "football" and the history of the sport, but alas, these facts were lacking from my formal education and aren't important enough for me to Google.
http://en.wikipedia.org/wiki/Mob_football
http://en.wikipedia.org/wiki/Medieval_football
"By some accounts, any means could be used to move the ball to a goal, as long as it did not lead to manslaughter or murder."
UPDATE/EDIT: The "socker pitch for scale" might be the 2 pixel wide small dot, almost indistinguishable from the beginning of the curved arrow pointing towards the blown-up version of the soccker pitch. One can hardly see it in the zoomed version of the image, with a little bit of imagination.
(ILC overall length: 31km, 724 pixel. Socker pitch: 80 pixel, 31km / 724px * 80px = 3.42 km; a vector drawing corresponding to the screenshot can be found in the technical design report, Volume 1, §3.1.1, fig. 3.1)