Yosef Karo

“ And it's permitted to talk with an outcast or excommunicate, unless the beit din excluded this explicitly.
Rema: But in any case one should not talk too much with him, and only talk with him out of necessity, like one talks with a mourner (Hagahot Alfasi and Rivash ibid.) . In the place it's forbidden to sit within his four amot, whenever a person sits first then the outcast comes there, he needn't move away from there (BY in the name of the pamphlet) . And it's forbidden to enter his house, as it's considered his four amot, and there's no difference between standing or sitting (ibid) . ”

“ Also those who perform labor whilst there is a corpse in town that is still not buried: they are liable excommunication, unless there are [burial] teams in town.
Also whoever makes leniencies or stringencies, or a gezeira shawah to uproot a thing from the Torah, or who asks an impossible question. Also whoever is wary of his fellow in some matter and turns him in to the king or judge, we ostracize him till he comes forth and stands in beit din. Also a talmid chakham who holds fast in a dispute against the majority. Also whoever gives a ruling in place of his rav. ”

“ Whereas an excommunicate neither teaches nor do we teach him, is not hired and we do not hire for him, and also we do not provide him any more pleasure than vital necessities (responsum of Rashba) . But he teaches himself so that he not forget his learning, and makes himself a little store for his sustenance. ”

“ When the person swearing or making vain blessing does it intentionally. But if by mistake and not knowing it's forbidden, it's forbidden to outcast him.
סעיף לח בד"א כשהיה הנשבע הזה או המברך לבטלה מזיד אבל אם היה שוגג ולא ידע שזה אסור אסור לנדותו. ‎
39 One who outcasts his fellow unlawfully, then furthermore tells him the nidui of another person is nidui:
This [amounts to] the statement that the second person's [nidui] takes precedence.
Or he doesn't know who it is, for we suspect he is (although unreliable (MHRIK #158) ) a greater rav than the [first one] one outcasting. ”

“ He shall afflict himself in view of all who see him. But he need not isolate from people, not in eating, drinking, or greetings. So he need not practice any of the mourning rules, and needn't appease the one who he was brazen to. ”

“ If Shimon outcasts Reuven so that he pays him, his nidui stands.
Rema: Some say a man should not bring judgment on his soul by casting out his fellow because of money (ibid. #25 in the name of MHRM and RABD) . This is the main thing, as it's written, "If your fellow expresses willingness to listen to the law..." (MHRYN #229) .
סעיף מו ראובן שחייב לשמעון ממון ומסרב מלפרעו אם נידה שמעון לראובן שיפרענו נידויו נידוי.
הגה: וי"א דלא עביד אינש דינא לנפשיה לנדות חבירו על דבר ממון (שם שורש כ"ה בשם מהר"מ וראב"ד) וכן עיקר כ"ש אם חבירו אומר להיות ציית דין (מהרי"ו סימן רכ"ט) . ”

“ Rema: And the Bit Din has permission to be severe with him, that no one circumcises his sons, and to not bury him if he dies (Binyamin Zeev #289 and כ"כ הב"י in the name of Ramban #244) , and expel his children from school and his wife from synagogue, until he accept the judgement (N"Y perek Hagozel) .
סעיף ו אם רצו בית דין למעט הנידוי מל' יום או להוסיף הרשות בידם.
הגה: ויש רשות לבית דין להחמיר עליו שלא ימולו בניו ושלא יקבר אם ימות (בנימין זאב סי' רפ"ט וכ"כ הב"י בשם הרמב"ן סי' רמ"ד) ולגרש את בניו מבית הספר ואשתו מבית הכנסת עד שיקבל עליו הדין (נ"י פרק הגוזל) . ”

“ And for the concern of nidui, witnesses and clear proof are not needed.
But rather, mental estimation of truth of the matters, that the accuser asserts it clearly, then even a woman, even a minor is believed, if awareness provides that the thing is true.
סעיף מג על כ"ד דברים מנדין את האדם ואלו הן:
א' המבזה את החכם אפילו לאחר מותו. ב' המבזה שליח ב"ד. ג' הקורא לחבירו עבד. ד' המזלזל בדבר אחד מדברי סופרים וא"צ לומר מדברי תורה. ה' מי ששלחו לו ב"ד וקבעו לו זמן ולא בא. ו' מי שלא קבל עליו את הדין מנדין אותו עד שיתן. ז' מי שיש ברשותו דבר המזיק מנדין אותו עד שיסיר הנזק. ”

“ Disparaging a messenger of the beit din. 3. Calling his fellow an `eved. 4. Belittling any one thing from divrei sofrim, needless to say divrei Torah. 5. Being summoned by the beit din and not coming. 6. Not accepting the judgement; he's outcast until he gives. 7. Possessing an instrument of danger; he's outcast until he removes the harmful thing. 8. he who sells his immovable property to an idolater is ostracised until he will assume responsibility of any mishap that may be brought about by the idolater against his fellow, the Israelite, his erstwhile adjoining neighbor ”

“ Outcast by all Yisrael is not outcast to the chief.
סעיף כא מנודה לנשיא מנודה לכל ישראל מנודה לכל ישראל אינו מנודה לנשיא. ‎
22 It has become the practice to not practice nidui, for transgressing a community's decree, with cherem or nidui until he's publicly announced. ”

“ Rather, people distance him in order to shame him, but he needn't practice mourning.
סעיף יב הא דאמרינן במנודה סתם שהוא אסור בדיני המנודה דוקא מנודה לב"ד שהוא מנודה לכל אדם בין דלא אתי לבית דין או דלא ציית דינא או לאפקירותא או לדבר עבירה בין נידוהו בית דין בין שנידהו כל אדם דינו שוה בין לעירו בין לעיר אחרת אבל מנודה לחצאין כגון תלמיד שנידה לכבודו וכן מנודה לעיר אחרת שנידוהו לכבודם אינו אסור בכל דין המנודה אלא שבני אדם מרחיקין אותו כדי לביישו אבל אבילות אין עליו. ‎
13 What we said, a regular Nidui is thirty days, is namely regarding when we outcast him, "So-and-so will be in Nidui thirty days." ”