well thats a fair point scule, but do you really think that idly throwing rocks in a spare few moments (even if there are rules) is what people mean when they use the word sport? If you meet someone at a party and they ask what sports you play, is that the response they are looking for?
Maybe we have to agree to disagree here, but I would consider the throwing rocks example as a game, and I think a game has to undergo a certain evolution before it can truly be considered a sport.