I find the concept of winning in a game really puzzling. Consider two games: checkers and kechers. In checkers, you win by the opponent having no legal move (this can happen two ways: all of the opponent's pieces are captured, or all of the opponent's pieces are blocked). In kechers, you win by not having a legal move. All the other rules of checkers and kechers are exactly the same. A legal game of checkers looks exactly like a legal game of kechers, and vice versa. Wherein the difference?
There are many possible answers: players' intentions, social context, language, etc. I think some of the answers end up being circular. Others fail because they fail to explain why it is the case that whenever x and y are playing checkers, they each have a prima facie reason to bring it about that the other has no legal move.
Here is a suggestion. We have a God-like power of creating ends (of course, like every power of ours, it is exercised only by the concurrence of God). When I come to participate in a game of checkers, I create a new end for myself, the end that the other have no legal move. Its objectively being an end of mine, I have reason to pursue it, and others have reason to wish me well in the pursuit of it. To be an end is not just to be pursued, of course: it is to be such that one have reason to pursue it.
Kantians, of course, will not be at all puzzled by the idea that we can create new ends for ourselves. But they will be puzzled by my next move. This next move is one that I make in response to the following second question: "How do we distinguishes cases where an end that we create is a victory condition for a game, from cases where it is not? How are games distinguished from other pursuits?" On the suggestion I want to explore, the answer to this question is very simple: We do not distinguish these. All and only the ends we create for ourselves are victory conditions for games. To play a game is to strive to win (so someone who throws a match is not really playing), and to strive to win is to pursue a self-created end. So now we have a story about what games are and how they differ from other pursuits: A game is a pursuit of an end that I have created for myself.
But aren't there other cases of ends that we can create, besides games? Can we not, say, set ourselves the end of becoming a great biologist, or an amateur astronomer, or the fastest draw in the West? In each case, I will say this: To the extent that the goal is valuable independently of our end-creation (it is valuable to understand living beings, to study the heavens even if only in an amateurish way, or to be able to defend the innocent), to that extent one is not playing a game. But insofar as the end achieves additional value through our making it our end (it is valuable for anyone to be a great biologist, but perhaps especially so for those who set out to become such), thus far we are playing a game, perhaps a solitary one.
But games don't matter deeply, while some ends we set for ourselves do matter deeply! Take love: If I choose to marry one person rather than another, then I make this person's happiness into an end of mine. I create an end for myself here, surely. Or take art: I accept a genre, and I work within it—I thereby create a genre-relative end, but that end is surely not just a game! However, these worries are mistaken. Consider love. First, I already ought to pursue the happiness of every human being—I ought to love my neighbor as myself. Second, insofar as I come to pursue a special marital end, it is because I am called to it—or at least, I come to be called to it when I undergo the sacrament of matrimony. If I weren't called to it (either generally, in the way I am called to love all neighbor, or more specifically), it would be a game—or a self-deception. Now consider art. Here, I am quite willing to say that insofar as one isn't pursuing some end independent of one's creation (beauty, truth, etc.), thus far one is playing a game. But it is important to note that while games may not matter deeply, they do in fact matter.