In the third chapter of Tractate Bava Kamma, we continue discussing the laws of Bor and the public domain. This short Mishnah contains two separate topics, and we will address each one in order.
The First Topic - Pouring Water in the Public Domain:
"Hashofech mayim birshus harabim vehuzak bahen acher chayav binizko" - a person who poured his wastewater into the public domain, and another person slipped on the water and was injured, is liable for the damage.
The novelty here is not that one who places an obstacle in the public domain and causes someone to slip is liable; that is not a novel ruling at all. The novelty is that this applies even when the action itself is permitted. During the winter season, halachah permitted pouring wastewater into the streets, because the streets were already full of mud and grime, so this does not worsen the existing situation - and pedestrians also took this into account, since it is the rainy season and everything is soaked and muddy. Nevertheless, if someone slipped and was injured as a result of the pouring - an injury that would not have occurred otherwise, such as if it was a dry day and the one pouring made the area slippery - the one who poured the water is liable, because this is simply a Bor in the public domain.
From here we derive a general lesson: even when an action is permitted, a person bears responsibility if someone is injured as a result. There are things that one has the right to do, and yet it is proper to think twice before acting, since any damage caused by them - is his responsibility.
It is worth noting: if the pedestrian was not physically injured, but rather only his clothing was damaged - such as getting dirty, or even tearing during the fall - the pourer is exempt from paying for them. The basis for this is the Torah derivation mentioned in the introduction to the beginning of the tractate: regarding the damages of a Bor, the Torah specifies an "ox" - excluding a person who dies in it, Heaven forbid; and a "donkey" - excluding utensils. In other words, the owner of the Bor is liable for damage to animals, but is exempt for damage to utensils, which includes the victim's clothing.
The Second Topic - Hazards Placed in the Public Domain:
"Hamatznia es hakotz ve'es haz'chuchis, vehagoder es gidro bekotzim, vegader shenafal lirshus harabim, vehuzku bahen acherim chayav binizkan" - we have three cases before us: one who buries thorns or broken glass in the public domain; one who surrounds his fence with thorns (similar to barbed wire today); and a wall, such as a retaining wall around a house or field, that fell and spilled into the public domain. If a pedestrian is injured by any of these - the owner is liable for his damage, since this is his own property.
The Thorns and the Glass:
In the time of the Mishnah there was no organized garbage collection, and the standard practice was to bury dangerous waste in the ground. If a person buried it in a way that people could reach it and be injured - he is responsible. But if he buried it in a manner that is considered a reasonable and proper disposal of dangerous items, he is exempt from unexpected damage, such as if floods came and exposed what had been covered.
Surrounding One's Fence with Thorns:
This refers to a wall standing on the border of his private property but abutting the public domain, such that the thorns on its top are actually located within the airspace of the public domain. It turns out that he placed his thorns in the public domain, and therefore he is liable for the victim's damages.
However, if a person sets his wall back into his private domain, in such a way that even the thorns resting on top of it and protruding from it are entirely within his private property - he is exempt from paying for damages. This seemingly contradicts another law: One who digs a deep pit at the edge of his property, right up to the street line, is liable. This is because people walking in the street do not carefully calculate where they are heading, and thus he has set a trap for anyone who might deviate one centimeter from the line into the private property and fall into the pit - something that is forbidden to do, and one who does so is liable. But regarding a wall, the assumption is that people do not walk in close proximity to it: everyone knows that brushing against a wall causes scratches, and they must keep a distance from it. Therefore, as long as the thorns are resting on a wall and inside the private property, and do not protrude into the public domain at all - the owner is exempt.
A fence that fell into the public domain:
If a wall fell and created a hazard in the public domain - the owner is responsible to clear it. But if a passerby was injured before the owner had sufficient time to clear what fell - for example, the wall fell, and immediately afterward a traveler tripped over the stones that had just fallen - he is exempt. For what could he have done? He acted properly.
The case is different if he had already been warned: Beis din notified the owner that his wall was about to fall and he must clear it within seven days, and he did not do so, and subsequently the wall collapsed. Since he had the ability to act in advance - he is liable from the very first moment.
Our Mishnah deals with someone who retained his ownership of the wall, meaning he intends to take back the fallen bricks, as they have value to him, and he had enough time to clear the debris but did not do so - and then someone was injured. But if he did not have enough time, or if he declared his wall ownerless and said: The wall is broken and I do not want it, I did not throw it here but rather it arrived there due to an accident, and I hereby declare it ownerless - as long as he officially declared it ownerless and removed his ownership, he is no longer responsible, and if someone is injured - he is exempt from paying.
In summary: In this Mishnah, we learned two topics. The first - one who pours water in the public domain is liable for the damages of anyone injured by it, and even when pouring is permitted, since this is considered a pit in the public domain; on the other hand, he is exempt for damages to utensils and clothing based on the exegesis **"shor"** - an ox, and not a person, **"chamor"** - a donkey, and not utensils. The second - one who hides a thorn or glass, one who builds his fence with thorns, and a wall that fell: the one who is liable is the person who placed the hazard within the public domain or its airspace, or who had sufficient time to clear it and did not clear it; and the one who is exempt is the person who removed its danger in the proper manner, one whose thorns are completely contained within his property, one who did not have time to clear it, and one who legally declared his property ownerless.