There's an easy way to distinguish "game of skill" from "game of chance" - just ask yourself: "Is there a World Championship for that game?"

Championships are organized only for games of skill, where you can have at least some chance of predicting the game outcome, make spectators care about this or that player. No one in their right mind would organize the championship in coin flip, or in MegaMillions lottery, because those game are pure chance, you can play them for decades and your chance of winning will be no better than that of a beginner. It would be hard to promote someone as "MegaMillions champion".