Gemara

15b: Since half-damage is a fine, if a dog ate a (large) sheep, this is abnormal (hence a Toldah of Keren), so we do not collect it in Bavel (like all other fines). If the victim seized payment, we do not make him return it.

If the victim requested to fix a time to go to Eretz Yisrael to judge the case, we comply. If the damager does not agree, we excommunicate him.

In any case, we excommunicate him until he removes the damager.

91a (Mishnah): If Levi spat at David, and the spit reached him...

(Rav Papa): If the spit did not land on him, only on his clothing, Levi is exempt.

(R. Yosi bar Avin): in any case, this is no less than verbal Boshes (embarrassment)! Our Mishnah teaches that one is exempt for verbal Boshes.

Rishonim

The Rif and Rosh (6a and 32b, 1:20 and 8:15) bring the Gemara.

Rif (30b): The custom of two Yeshivos is that we do not collect fines in Bavel, but we excommunicate until he appeases the victim as Beis Din deems proper, then immediately permit the Cherem, whether or not the victim was appeased.

Rosh (8:2): Perhaps this was an enactment of Ge'onim. This is unlike the Gemara. Niduy is the ultimate collection! The Gemara says that we excommunicate until he removes the damager (but not until he pays).

Rambam (Hilchos Sanhedrin 5:17): The custom of Yeshivos in Chutz la'Aretz is that even though we do not collect fines, we excommunicate until he appeases the victim or goes to Din with him in Eretz Yisrael. Once he gives the proper amount, we permit the Cherem, whether or not the victim was appeased.

Rosh (1:20): The Ra'avad says that we do not collect fines in Bavel, but we excommunicate until he appeases the victim as Beis Din deems proper. If there is a fixed amount, e.g. 50 Shekalim for rape, he must pay it. This is unclear. We excommunicate only if the victim asks to go to Beis Din in Eretz Yisrael, and the damager refuses. Also, Niduy until one pays is the ultimate collection of fines!

Rosh (8:3): Mar Tzemach Gaon said that even though generally we do not collect fines in Bavel, we do not want sinners to profit, and that people will wantonly rape, entice and steal. Therefore, the custom of latter Chachamim is to excommunicate until he appeases the victim with money, or brings friends and verbally appeases him. Once, Levi knocked out David's tooth. Mar Rav Tzadok Gaon did not fix an amount; he told Levi to appease David with words or money. Nowadays, all fines are Batel. The custom is like Rav Tzadok Gaon. R. Natrunai Ga'on said that nowadays if one wounds, we do not make him pay the value of the limb, we excommunicate him until he appeases him, with much or little. Rav Shrirah Gaon says that the Gemara says that we excommunicate only until he removes the damager. Latter Chachamim saw a great loss through not collecting fines, and enacted to excommunicate until he pays close to the proper amount. We cannot be exacting to say how much he must pay before the victim must forgive. Rather, we estimate, and do not tell him. We excommunicate him until he appeases the victim. If he gives close to what the judges thought and the victim is not appeased, we cannot excommunicate him any longer; we permit him. If it is far from what we thought, he is in Niduy until he gives close to it.

Yam Shel Shlomo (8:6 DH ul'Inyan): The Tur (EH 177) rules like Rav Tzemach Gaon, who excommunicates a rapist or enticer until he appeases her father, lest a sinner profit. This is difficult. The fine applies only through witnesses. No one ever heard about Ones u'Mefateh in front of witnesses! We did not enact for something so rare; also, there is no Chisaron Kis. It is proper to excommunicate until he pays pain and Boshes. There is no Chisaron Kis, but the bodily pain and Boshes is more than property damage; it is like Chisaron Kis. The Halachah follows Rava, who is not concerned lest a rapist or enticer profit (Kesuvos 11a). Even though wounding is more common, we do not want a sinner to profit and shame Bnos Yisrael, and empty people should not be Perutzim in Zenus. Perhaps Rav Tzemach Gaon meant that we excommunicate only for Boshes and Pegam. Even if all laws of a rapist require three expert judges, it is proper to force him to marry her, even if we must use Nochrim. We force anyone to fulfill a Mitzvas Aseh!

Rosh (15): Rav Shrirah Gaon says that we excommunicate even for verbal Boshes, until he properly appeases him according to his honor.

Poskim

Shulchan Aruch (5): Judges without Semichah in Eretz Yisrael do not collect fines in Bavel, but we excommunicate until he appeases the victim. Once he gives the proper amount, we permit the Cherem (Rema - whether or not the victim was appeased). If the victim seized the proper amount, we do not take it from him.

SMA (17): Presumably, the Shulchan Aruch means like the Tur and Rosh bring in the name of Rav Shrirah Gaon, that he gives close to the proper amount. This is why the Shulchan Aruch continues 'if the victim seized the (full) amount that he is owed, we do not take it from him. 'What is proper' (regarding seizure, but not regarding Cherem - PF) includes Kefel, four or five. The Shulchan Aruch teaches that even though we do not collect fines, there is a Tikun through Niduy, and through Tefisah.

SMA (18): The Ir Shushan says that we do not permit the Niduy until he gives close to Kefel, four or five. This is wrong. In Siman 348, no one says that Niduy lasts after he pays the actual damage. The Tur says that it was an enactment lest people wound each other. It suffices to obligate principal.

Shach (14): We excommunicate only for things like wounding, for which one pays only principal. If not, everyone will damage. We do not excommunicate for Kefel, four or five (for in any case people refrain).

Yam Shel Shlomo (8:6 DH Kosav and Sof DH Lachen): The Rif's enactment is proper for wounding and quarrels. The Rosh leans to rule like Rav Shrirah Gaon, who excommunicates until he gives close to our estimate. Rav Shrirah Gaon said Stam 'fines', but he refers only to wounding and quarrels; he says that it is so a sinner will not profit. He does not refer to Kefel, four or five, and not to Keren, for Stam oxen are guarded. Chachamim need not enact for half-damage, which is a fine. We do not enact even for a pit or fire. We enact only for wounding, Boshes, or property damage through theft, which we do not collect in Bavel. The judge must be careful that the kingdom not hear, lest they assume that there was negligence and punish greatly. This could endanger other Yisre'elim! Even the Rif meant only matters like I said. He mentions 'whether or not the victim was appeased', which applies to wounding. The Rosh (1:20) argued with the Ra'avad (who excommunicates for all fines); he did not bring the Rif. In Perek 8 he cites the Rif without dissent, and suggested that perhaps Ge'onim enacted like this. We set a time to pay; he is in Niduy if he does not pay within the time.

Shulchan Aruch (6): If one embarrassed verbally, we excommunicate him until he properly appeases the victim according to his honor.

Ir Shushan (6): One is liable for verbal Boshes, just we do not collect for Boshes in Bavel; we only excommunicate until he appeases.

Rebuttal (SMA 22): Letter of the law one is exempt (even in Eretz Yisrael).