We played, at one point, an Aztec game with d20 rules. It didn't work out too badly. We used, essentially, combat mechanics, with some extra bits for throwing and catching the ball. Most of it seems pretty similar to Klaus's suggestions, though what we played had a smaller goal (more like a sideways basketball hoop than a soccer goal, so I believe it was a Tiny target).
Some of the players played our characters, and the rest of the players were the opposing team - the DM had written up stats for opposing players, who were mostly monks, as I recall. We had quite a bit of fun with it.