Are there any important halachic issues related to gambling--specifically, on card games? (I'm thinking Texas Hold 'Em, but kvitlach also comes to mind.)
Obviously it can't be done on Shabbos or Yom Tov. Anything else to be aware of?
If it is being played for money there is an issue of stealing.
The source for gambling in general is found in the Mishna in Sanhedrin (24b-25a)
See this site:
The Halachic Prohibitions Involved in Gambling
The Mishnah in two separate places addresses the issue of the worth of a gambler's testimony in a Jewish court of law.
In Tractate Rosh Hashanah Chapter 1 Mishnah 8 the Mishnah lists those that are disqualified from giving testimony about the 'new moon'. Among the others that are mentioned are two categories of people that concern us.
(a) 'Mesahakei Kubia' literally dice players or gamblers.1
(b) 'Mafrihe Yonim' literally pigeon-fliers or pigeon racers.
Both categories are disqualified to give testimony about the new moon in the Beth Din - the Jewish Court.2
In Talmud Sanhedrin another Mishnah, in which there is a debate between the Hakhamim (Rabbis) and Rabbi Yehuda dealing with the ineligibility of these two categories of individuals from being judges or giving testimony3 in monetary cases is quoted as follows:
These are the ones ineligible to be judges or witnesses: One who plays with dice, or pigeon fliers. Rabbi Yehudah said When are dice-players ineligible to adjudicate or testify? When they have no trade but this, but if they have a trade besides this they are eligible.
Rashi explains Rabbi Yehudah's view as people whose sole occupation is gambling are not involved in doing anything useful. As a result, they are unacquainted with basic business law and commerce, and have no aversion to illegal activity. However, one who engages in some other form of occupation is not flawed in this way and remains eligible.
The Gemara bring down a debate about why a dice-player's activity disqualifies him:
Rami Bar Hama says that the dice player is disqualified because the wager agreement he is entering into is an example of asmachta4, because each player consents to the terms of the game only because he expects to win. Since the loser does not willingly surrender the wagered amount, the winner is considered to be stealing when he collects, and is thus ineligible as a witness or judge.5
Rabbi Sheshet says this agreement is not considered an asmachta. According to this opinion the only situations that involve asmachta are when the individual relies on his own ability. Dice players realize that the outcome of the game is determined by chance and not their own personal skill6. Rather, dice players are disqualified because they are not involved with furthering the general welfare of society.
The Talmud explains that the difference between these two opinions is the case where the gambler learned another profession.
Rami bar Hama would still disqualify the gambler by virtue of his accepting winnings based on a non-binding asmachta agreement, whereas according to Rav Sheshet he is eligible because his second occupation is socially useful.7
According to Rami bar Hama the prohibition involved in gambling is not the gambling itself but taking the winnings which involves the 'dust of robbery'.
According to Rav Sheshet there is no prohibition in taking the winnings, the problem is being a gambler. This occupation is distasteful as is non productive.
The Rambam8 (Hilchot Gezela Chap. 6 Halacha 10) codifies that gambling between two parties is Rabbinically prohibited as it is classified as robbery by the Rabbis. Even though the winner took the proceeds with the full knowledge and consent of the loser, since he took his money for nothing, by playing, it is considered robbery. Similarly, wagering on animals and birds is prohibited rabbinically.
However the Rambam in Hilchot Edut9 says that a person who plays dice is disqualified from giving testimony only if he is a professional gambler and has no other occupation, since he is not engaged in settling the world. He must be living of the proceeds of his gambling which is the 'dust of robbery'10. Similarly a person who wagers on animal and bird races is disqualified if he has no other occupation except this.
The Shulhan Arukh follows the opinion of Rambam by classifying gambling as asmachta which would mean that the winner is not entitled to the proceeds of his victory and retaining would be considered stealing.**22 **However, like Rambam, he also only disqualifies the gambler as a witness if gambling is his only means of livelyhood,23 thereby creating the same compromise between Rab Sheshat and Rami Bar Hama as did Rambam. The Remah however disagrees with the Shulhan Arukh and decides the law according to the Tosaphot and Mordecha, The Tosaphot and the Mordechai16 explain that even according to the above mentioned opinion which permits "Dice Playing" as long as one has another profession, it is only permitted to do so if the actual cash is placed on the table and the money is transferred to the winner immediately follwing his victoryi.24
There is a further issue of wasting time:
The Minhat Yitzhak49 discusses the general implications of playing games in general. He quotes the classic ethical work Reishit Hochma50: "Included in a session of scoffers51 are those that play dice and other games, even though they do not play for money, which is prohibited because of robbery, it is considered a session of scoffers
Cards are not specifically mentioned in Gemara as far as I'm aware but there is a mention of players of dice games, in Sh'vuot, where it says that such people are not acceptable as witnesses (to claim money owed to them or admit to a partial debt in court when the disagree on the full amount).
And it means they play dice for money (e.g. craps or whatever they played back then) not backgammon or monopoly or whatever for leisure.
I am not sure exactly how it would to poker, which has a skill element to it such that a good player will win in the long run. (They won't win more games but they'll win more money because they'll fold earlier on losing hands more often).
In particular, if you enter a tournament where you pay an entry fee, and the winner gets prize money, that is probably not considered gambling.
However given that the Gemara (Rosh Hashanah, on giving testimony for the moon) mentions "professional" gamblers as detrimental to society, I will assume they did play games with a skill element such that the "professional" would win more than they lose, otherwise they could not make a living out of it. And also suggests that only such people are not allowed to give testimony.
As has been discussed previously:
The Gemara in Sanhedrin asks why "dice gamblers" are invalidated from being witnesses. One explanation is that when people gamble they're not entirely cognizant of the likelihood they'll walk away with a loss, so it's ill-gotten gains. The other explanation is that it applies only to those who are professional gamblers, "as they aren't among those who help civilize the world."
There's a lot of halachic discussion about the parameters of the first reason -- what sort of commitment was made to pay up -- verbal, or something more formal? Maybe people are more aware of the risks if it's entirely a matter of luck (e.g. fair dice) rather than skill, where we are so incredibly good at deluding ourselves that we're "better than average."
The Mishna in Shabbos also discusses some sort of lottery; Rabbi Ovadiah Yosef's opinion is that it's outright prohibited not just on Shabbos (because it looks like financial matters), but on weekdays as well.
The Aruch HaShulchan concludes that while many cases of gambling are technically allowed, as a seasoned rabbi he's seen it destroy a lot of lives.
The Chochmas Adam specifically discusses someone who has a gambling problem and has taken an oath not to play cards. If the oath was because he's been losing money, then he's still allowed to play without money. If the oath was because he's losing all his time and getting into fights, then he can't even play without money.
Chavos Yair 126 mentions that in his town, the rabbis enacted a policy to ban playing cards [I assume for money], except on Chanukah. This disturbed his father as that's how we celebrate a Jewish holiday?! Yet I've seen Hassidic Jews today who still do so -- only on Chanukah.
In short -- it may very well be prohibited in the Sephardic world. In the Ashkenazic world, it's been around a long time and recognized as a very dangerous vice.