Short answer. As a game of chance. Article 2013 defines a game of chance as one depending more on chance or hazard than on skill or ability, and provides that in case of doubt a game is deemed to be one of chance. The doubt is resolved against the game, so the stricter gambling rules apply.
What the law says
A game of chance is that which depends more on chance or hazard
Civil Code, Article 2013 — Game of Chance Defined. Read the full provision →
What the law says
in case of doubt a game is deemed to be one of chance
Civil Code, Article 2013 — Game of Chance Defined. Read the full provision →
Doubt is resolved against the game
Article 2013 does two things in one breath. It defines the category — A game of chance is that which depends more on chance or hazard than on skill or ability — and then it settles the hard cases with a presumption: in case of doubt a game is deemed to be one of chance. The test is not whether skill plays any part at all, since almost every game involves some, but which force predominates. Where that balance is genuinely unclear, the law does not leave the question open. It tips the scale one way, treating the game as one of chance until shown otherwise.
Why the classification decides everything
This definition is not an idle one; the articles that follow it hang on the label. A game of chance carries its own regime — the winner cannot sue to collect his winnings, while the loser is allowed to recover what he paid, and those who merely bet on such a game are treated like the players. A game of skill is not swept up in that machinery. So whether an activity is one of chance or of skill is not a philosophical nicety: it decides who can go to court and for what, which is precisely why Article 2013 refuses to let a doubtful case escape classification.
Where the line actually falls
Predominance is the working test. A game whose result turns mainly on the fall of cards, a wheel, dice or a draw is one of chance even though a shrewd player fares better over time. A contest decided mainly by the participants' ability — their calculation, physical skill or judgement — is one of skill even though luck can swing a single round. Many popular games sit uncomfortably between the two, mixing wager, ability and randomness, and it is exactly those that Article 2013's tie-breaker is written for: when reasonable minds could go either way, the game counts as chance.
What this means for a dispute
If you are arguing about money won or lost, the classification is the first thing to pin down, because everything else follows from it. The party resisting recovery will press that skill predominated; the party seeking it will press chance, and will have the presumption on his side where the matter is doubtful. What tends to decide these disputes is a clear account of how the particular game is actually won — what the outcome really depends on in play — rather than the name the game happens to go by.