Its at worst a venial sin IMO, though one should never wish to do any sin for any reason. However, though clear, repeated, and certain venial sins ought to perhaps be anticipated and avoided, the general consensus of theologians seems to be that we should not worry too much about the mere possibility of venial sins happening, despite trying to constantly purify ourselves. Also, you might want to account for the ‘situation that will likely make you angry’ and not too quickly judge that it is simply ‘playing a game’ that is the situation that causes it. Do a little analysis of it.
Perhaps you could use this as an opportunity to regulate the causes of your anger. The anger seems to be a sign of the great importance you put on winning a game in such a trivial matter and a sign of a lack in trust in God’s providence in small matters. I wouldn’t necessarily say get rid of the games, but perhaps play them in moderation with a greater sense of peace in God’s providence in every thing (however small) in life and the realization of the unimportance of what you wish the outcome of the game to be. Its a chance to exercise humility in defeat too :D.