I played this with a friend, and this is the best multiplayer dungeon crawler I've ever played (of, well, maybe 2 total...). We had a lot of fun with this, and I really like how the duality is integrated into the gameplay, there was some real developing of skill managing our dual players as we played a few rounds. Only thing I would have wished for was slightly more feedback on having the ball or not, occasionally I'd run past him, think that I grabbed the ball, and make it a few steps before realizing I didn't have it. Maybe just a solid sound effect whenever the ball exchanged hands would be good, although maybe it's hard for that to work when both teams are hearing the same sounds ^_^.
As for whether or not it matches the rules, maybe it all comes down to the question: Is soccer inherently combat to resolve an enemy encounter? =)
Also of note, both of our hands got quite sore after only a few rounds, this needs controller input ;).