  During last years poker has gained a lot of prestige in several countries
and, beyond to be one of the most famous card games, it represents a modern
challenge for scientists belonging to different communities, spanning from
artificial intelligence to physics and from psychology to mathematics. Unlike
games like chess, the task of classifying the nature of poker (i.e., as 'skill
game' or gambling) seems really hard and it also constitutes a current problem,
whose solution has several implications. In general, gambling offers equal
winning probabilities both to rational players (i.e., those that use a
strategy) and to irrational ones (i.e., those without a strategy). Therefore,
in order to uncover the nature of poker, a viable way is comparing performances
of rational versus irrational players during a series of challenges. Recently,
a work on this topic revealed that rationality is a fundamental ingredient to
succeed in poker tournaments. In this study we analyze a simple model of poker
challenges by a statistical physics approach, with the aim to uncover the
nature of this game. As main result we found that, under particular conditions,
few irrational players can turn poker into gambling. Therefore, although
rationality is a key ingredient to succeed in poker, also the format of
challenges has an important role in these dynamics, as it can strongly
influence the underlying nature of the game. The importance of our results lies
on related implications, as for instance in identifying the limits poker can be
considered as a `skill game' and, as a consequence, which kind of format must
be chosen to devise algorithms able to face humans.
