What is the X in X-mas?
open-air game, first recorded c.1400; see foot (n.) + ball (n.1). Forbidden in a Scottish statute of 1424. The first reference to the ball itself is late 15c. Figurative sense of "something idly kicked around" is first recorded 1530s. Ball-kicking games date back to the Roman legions, at least, but the sport seems to have risen to a national obsession in England, c.1630. Rules first regularized at Cambridge, 1848; soccer (q.v.) split off in 1863.
The U.S. style (known to some in England as "stop-start rugby with padding") evolved gradually 19c.; the first true collegiate game is considered to have been played Nov. 6, 1869, between Princeton and Rutgers, at Rutgers, but the rules there were more like soccer. A rematch at Princeton Nov. 13, with the home team's rules, was true U.S. football. The earliest recorded application of the word football to this is from 1881.