piedpilko

The base word the rest of the family was waiting for. Piedo is foot, pilko is ball, and welding them gives you piedpilko: the ball, and by the usual extension the game played with it. Piedpilkado at rank 2134 is the same thing with -ad- on the end, which shifts it to the playing of the game as an activity, and that is the form the frequency list met first. If you are talking about a match or the object itself, piedpilko is the word; if you are talking about the sport as something people do, piedpilkado is.

The honest bit, and it is the same on all three pages: most speakers say futbalo. Futbalo is the international borrowing, it is what PIV leads with, it is what the Esperanta futbala teamo calls itself, and it is what you will hear in a bar. Piedpilko and piedpilkado are the home-built alternatives, favoured by speakers who would rather Esperanto assembled a word from roots you already own than imported a new one. They are perfectly correct and widely understood. Some writers use the pair to draw a line: futbalo for association football, piedpilko for the wider family that takes in rugby and the American and Australian codes.

Why it is worth learning both. This is la bona lingvo argument in miniature, and it is a permanent, cheerful quarrel rather than a question with an answer. Knowing piedo and pilko gets you piedpilko for nothing; futbalo has to be memorised but is already in the Brazilian's and the Pole's heads. Both positions are held by fluent people, which is the tell that neither is silly. The adjective from this side is piedpilka, and a player is a piedpilkisto.