Commentary for Bava Kamma 11:24

If [you would say so] regarding the pit which [was dug] without permission. It appears from the Gemara’s refutation that the bor discussed in the Torah was never allowed to be there and it is always illegal. What about a bor that a person dug on his own premises? He certainly was allowed to dig it on his own property. Later at some time he relinquishes ownership of that property and it becomes part of the public domain. Here it seems that we have a situation where the bor was created legally and even so the original owner is liable. Why does the Gemara say that the presence of a bor in the public domain is always illegal? Tosafot explains:
For even if the bor was made legally in the bor owner’s property and afterwards he relinquished his ownership, as soon as he relinquishes ownership and he allows the public access to the bor, that is illegal. The very act of relinquishing ownership which gives the public access to a bor that could harm them is illegal. See Otzar HaTosafot note 985 who elaborates on this matter.

Would you say [the same] regarding these [which were dug] with permission? [The case of] the ox proves [otherwise]. When faced with the refutation that bor is liable because it was illegal to have the bor in a public domain as opposed to emptying the waste pipes or allowing the sewage into the public domain which is legal and therefore one might not be liable, the Gemara presents shor as proof that one may legally be in the area where the damage occurred and still be liable. The shor may of course be in the public domain and even so he is liable for damaging. Tosafot scrutinizes the assumption that the shor’s presence in the area that he damages is legal.
And if you ask: According to the one who holds that the Tano of our Mishna taught shor to inform us that he is liable for damage he causes with his regel, how does the Gemara say that shor proves that even when one is legally in the place that he damages he is liable, but regel is only liable when the ox damages on the property of the victim and he has no legal right to be there?
And we can answer: the regel to which the Gemara is referring is for example, the animal was walking in a public domain and it causes stones to jump and subsequently the stones damaged vessels in a private domain bordering the public domain for which the ox owner is liable, as the Gemara says later on Bava Kamma 19a. It was legal for the ox to be in the public domain and even so his owner is liable. This proves that one can be liable even if it was legal to be in the place where he caused the damage.