Gemara

(Mishnah): If a judge acquitted the guilty or obligated the innocent, or declared what is Tahor to be Tamei or vice-versa, the verdict stands, and he pays for the loss he caused.

A Mumcheh (expert) authorized by Beis Din is exempt.

Suggestion: Our unauthored Mishnah is like R. Meir, who obligates for Garmi (causing damage).

Rejection (R. Ilai): It is like everyone. The case is, the judge himself executed his mistaken ruling and transferred the money from one party to the other.

Sanhedrin 33a (Mishnah #1): A monetary verdict can be overturned, whether Zechus or Chiyuv.

Contradiction (Mishnah #2): If a judge acquitted the guilty or obligated the innocent, what he did stands. He pays for the loss that he caused.

Answer #1 (Rav Yosef): Mishnah #1 refers to a Mumcheh. Mishnah #2 discusses an amateur.

Question: We do not overturn the verdict of a Mumcheh!

(Mishnah): A Mumcheh l'Rabim is exempt. (If he can overturn a mistaken verdict, there is nothing to pay for!)

Answer #1 (Rav Nachman): A bigger Chacham can overturn the verdict. If there is no bigger Chacham, the verdict stands.

Answer #2 (Rav Sheshes): If he erred bi'Dvar Mishnah (a clearcut mistake), we overturn the verdict. If he erred b'Shikul ha'Da'as (ruled unlike the primary opinion), the verdict stands.

Answer #2 (to the Contradiction - Rav Chisda): If the judge himself transferred the money, the verdict stands. If he did not, we overturn the verdict.

Question: Regarding 'he acquitted the guilty' he said 'you are exempt.' He did not transfer money!

Answer (Ravina): Almoni had a security of Ploni. When the judge exempted Ploni, he took the security and gave it to Ploni.

Rishonim

Rif: A mistaken ruling stands if the judge himself transferred the money, like Rav Chisda said. Also in Bechoros we established the Mishnah like this. The Halachah follows Rav Sheshes, who say that we retract from an error bi'Dvar Mishnah.

Rebuttal (Ba'al ha'Ma'or 10b): Since we obligate for Garmi like R. Meir, we do not establish the Mishnah to be when the judge himself transferred the money. We do not hold like R. Ila'a and Rav Chisda, rather, like Rav Yosef, Rav Nachman and Rav Sheshes. Rav Yosef, Rav Nachman and Rav Sheshes do not argue; they give different answers. The Halachah follows Rav Nachman in monetary laws.

Defense (Milchamos Hash-m): The Halachah follows Rav Chisda, for Ravina, who is Basra, answered for him. Rav Chisda explains the Mishnah like R. Meir. If he held like R. Ila'a, the Gemara would have said so! Rather, Rav Chisda teaches that the Halachah is that the verdict is reversed. The Ba'al ha'Ma'or says that we retract an error bi'Dvar Mishnah, for it was a total mistake and the one who asked should not have relied on it at all. This is wrong. Not all know every Sifra, Sifri, Tosefta and Gemara. Even a mistake about Amora'im's teachings is an error bi'Dvar Mishnah! Women and children do not know Halachos. How could they know not to rely on the ruling?! He also said that if the judge is not learned, even if the parties accepted him on them, it is not a verdict, whether or not he erred, whether or not he actively transferred the money. This connotes that even after the final verdict, he can retract. This cannot be. Even three shepherds who do not frequent settled areas cannot retract after the final verdict. Since they are utterly ignorant, they are no better than a lone judge. Since the parties accepted them, their verdict is a verdict. Also, if a party waived his rights to his opponent, he cannot retract, e.g. 'swear to me by the life of your head' (in place of a proper oath that he was required to take). This is whether he pardons his opponent from paying, or obligates himself to pay. All the more so, if one accepted an amateur judge, his verdict is a verdict if he did not err. If he erred, surely he retracts, whether or not he actively transferred the money.

Rosh (Sanhedrin 4:5, according to the Rif): We resolve the Mishnayos like Rav Chisda said. The judged erred in Shikul ha'Da'as. The verdict is reversed only if he did not hand over the money. When the judge is exempt, we reverse the verdict lest the party lose money.

Rebuttal (Rosh): The Mishnah in Bechoros exempts a Mumcheh. This refers to the Reisha, which says that the verdict stands, and therefore an amateur pays. Even so, a Mumcheh is exempt! Also, why did Rav Chisda need to say that he is liable when he transferred the money himself? He could have said that an amateur is liable! Also, we do not exempt a judge for mistakes, lest this deter people from lending. If the verdict is reversed, people would not be deterred even if the judge is exempt! Also, the Rif was forced to say that the verdict stands when the people did not accept the judge. The opposite is more reasonable! Also, a judge who has permission from the Reish Galusa is exempt. This implies that his verdict stands, yet permission exempts! The Halachah is unlike Rav Chisda, for he explains like Chachamim, but the Halachah follows R. Meir. Rav Hai Gaon says so. We establish the Mishnah like Rav Nachman and Rav Sheshes. Rav Nachman discusses one who erred b'Shikul ha'Da'as, like Tosfos says. We retract an error bi'Dvar Mishnah. The Mishnah in Bechoros is like Rav Yosef said, when he is not an expert. Even though a greater Chacham could change the verdict, since this judge pushed himself to judge, and he is not an expert, it is proper that the verdict stands and he himself will pay. Even though the parties accepted him, he should not have judged alone, since he is not an expert. Our Mishnah discusses an expert, therefore he does not pay and we retract the verdict if there is a bigger Chacham. The Seifa of the Mishnah in Bechoros discusses when there is no greater Chacham. Therefore, the verdict stands. A Beis Din can nullify another Beis Din's words only if they are greater in Chachmah and Minyan.

Rambam (Hilchos Sanhedrin 6:2): An error in Shikul ha'Da'as is when two Tana'im or Amora'im argue with each other, and the Halachah was not explicitly fixed like either one, and the judge ruled like one, unaware that everyone follows the other. If a Mumcheh made such an error and he had permission from the Reish Galusa, or he had no permission but the parties accepted him on themselves, since he is a Mumcheh, the verdict is reversed. If it cannot be reversed, the judge is exempt.

Rambam (3): If the judge was a Mumcheh but did not have permission from the Reish Galusa or the parties, or he was an amateur but the parties accepted him on themselves to judge properly, and he erred about b'Shikul ha'Da'as, if he transferred the money, what he did stands, and he must pay. If he did not transfer the money, the verdict is reversed.

Tur (CM 25): An error in Shikul ha'Da'as is when two Tana'im or Amora'im argue, and the Halachah was not explicitly fixed like either one, and the judge ruled like one, but the Sugya follows the other. E.g. the Stam Gemara asks a question based on the other opinion. Rashi says that most judges rule like the other opinion.

Poskim

Shulchan Aruch (CM 25:2): If a judge erred b'Shikul ha'Da'as, e.g. two Tana'im or Amora'im argue, and the Halachah was not explicitly fixed like either one, and the judge ruled like one, unaware that the entire world follows the other:

Shach (7): The same applies if Poskim argue. The Rosh and Tur discuss an argument 'of Gedolim.'

Shach (10): It need not be in the entire world. Everything follows the local custom, e.g. in the entire country of Rinus (near the Rhine River? - PF) they forbid Chelev on the Kerev.

SMA (10): The Darchei Moshe (6) brings Teshuvos Maimoniyos (Shoftim 8) that if the judge did not know there is another opinion, and ruled like the opinion that he knew, this is not called an error b'Shikul ha'Da'as. What he did stands, and he does not pay.

Shach (8): Also the Mordechai (Sanhedrin 713) says so. Many understand that later the judge heard the other opinion. Even though still he is unsure, they teach that this is not Shikul ha'Da'as. This is wrong. Rather, they teach about one who never heard the other opinion. This is a reason to exempt. This is clear from Hagahos Ashri (Sanhedrin 1:2), who obligates for Shikul ha'Da'as only if he knew that they argue. However, the entire law is difficult. The judge pays due to Garmi, which is even for Shogeg. Also, an error about learning is considered like Mezid. The Rif, Rosh and Nimukei Yosef connote unlike this.

Shulchan Aruch (ibid.): If the judge was a Mumcheh with permission from the Reish Galusa, or the parties accepted him on themselves, since he is a Mumcheh, the verdict is reversed. If it cannot be reversed, the judge is exempt.

SMA (14): This is like the Rif, who holds that when the judge is exempt, we retract so that the litigant will not lose. The Rosh and Tur hold that the verdict stands. The Rema did not bring the argument. He relied on what he wrote in Sa'if 3, that some say that the verdict stands, i.e. and the same applies here.

Shach (13): This is whether or not the judge acted to carry out the verdict. Also the Rosh, who argues, does not distinguish whether or not he acted to carry out the verdict.

Rema: Three commoners are like one expert.

Shach (14): The opinion of the Rosh and Tur is primary. Also Rav Hai Gaon, Ba'al ha'Ma'or, R. Efrayim and R. Yerucham rule like them. Ba'al ha'Itur and the Rosh brought many clear proofs for this opinion.

Shach (14, paragraph 18): I do not understand why in YD 242:31, the Rema rules like the Ran (Avodah Zarah 2a), who says that even for an error b'Shikul ha'Da'as, one can argue with the judge until he retracts. The Ran himself said that in practice, he cannot argue with the fathers of the world, i.e. the Ra'avad, Ramban and Rashba. The Rosh and R. Yerucham agree. Also, the Ran said this according to the Rif, who rules like Rav Chisda. We rule like Rav Sheshes! The Rema himself (Sa'if 3) says that some rule like Rav Sheshes.

Gra (Likut): This discusses an error b'Shikul ha'Da'as. We retract an error bi'Dvar Mishnah even if three experts judged and the litigants accepted them. It does not matter whether or not they acted to carry out the verdict, or whether or not there is someone greater than them. However, the Ra'avad holds that if they accepted a lone expert, he does not retract even if there is someone greater than him.

Shulchan Aruch (3): If the judge was a Mumcheh but he did not have permission from the Reish Galusa or the parties, or he was an amateur and the parties accepted him on themselves to judge properly, and he erred about b'Shikul ha'Da'as, if he transferred the money, what he did stands, and he must pay. If he did not transfer the money, the verdict is reversed.

Rema: Some say that even if he did not transfer the money, the verdict stands and he pays.