872. One Who Leaves His Techum on Shabbos

Shabbos 27:11

If someone goes even a single cubit beyond the Shabbos boundary, he may not reenter. Rather, he is granted his four personal cubits (about six feet) from the place where he is standing; he may only walk those four cubits. Similarly, if a person is even one cubit outside a city's Shabbos boundary when Shabbos arrives, he may not enter the city. Rather, he may proceed no more than 2,000 cubits from where he was standing when Shabbos began. Even if his Shabbos boundary lands in the middle of the city, he may not proceed beyond this limit. If one foot is inside the city's  Shabbos boundary when Shabbos begins, he may enter the city even though the other foot is outside.

Shabbos 27:12

If someone left their Shabbos boundary unintentionally, such as if he were brought outside by non-Jews or was possessed by temporary insanity, or if he simply made a mistake, he is then limited to four cubits. If he comes back within his original Shabbos boundary, he is still limited to four cubits but if the force that brought him out subsequently returned him, it's as if he never left. If the compelling force deposits him in a private domain, such as if non-Jews left him in a barn, corral, cave or a different city, then he may walk throughout the entirety of that domain. Similarly, if he accidentally left his Shabbos boundary and entered such a domain, and only then did he become aware of what he had done, he may walk throughout the entirety of that domain.