Liability for damage caused by a fallen wall or fence

Question

Who is liable for the damage caused if a person's fence or wall falls into public property? According to Bava Qama 3:2, if a person's fence falls into a public thoroughfare and somebody is harmed, the owner of the fence must pay compensation. According to Bava Metzia 10:4, if a person's wall falls into a public thoroughfare and somebody is harmed, the owner of the wall is exempt from paying compensation.

Is there an important difference between fences and walls of which I'm not aware? Or are these mishnayot simply speaking of different cases?

Here they are, with the relevant sections in bold:

השופך מים ברשות הרבים והוזק בהן אחר, חיב בנזקו. המצניע את הקוץ ואת הזכוכית והגודר את גדרו בקוצים וגדר שנפל לרשות הרבים והוזקו בהן אחרים חיב בנזקן

If somebody pours water in a public thoroughfare and somebody else is harmed as a result, he is obligated to pay compensation. If somebody hides thorns or glass [in a public thoroughfare], or places thorns in their fence [in such a way that they abut onto a public thoroughfare], or if a person's fence falls into a public thoroughfare and somebody is injured as a result, he is obligated to pay compensation.

• Bava Qama 3:2

וכן בית הבד שהוא בנוי בסלע וגינה אחת על גביו ונפחת הרי בעל הגינה יורד וזורע למטה עד שיעשה לבית בדו כפין. הכתל והאילן שנפלו לרשות הרבים והזיקו פטור מלשלם. נתנו לו זמן לקוץ את האילן ולסתור את הכותל ונפלו בתוך הזמן פטור, לאחר הזמן חיב

Similarly, regarding an olive press built on stone with a garden on top of it, if the roof caves in then the owner of the garden may plant below [on the floor of the olive press] until the owner of the olive press makes a roof. If a wall or a tree falls into a public thoroughfare and harms somebody, he [the owner of the wall or the tree] is exempt from paying compensation. Time is given him to chop up the tree and to mend the wall, and should it fall again within the allotted time he remains exempt, but if it falls after the allotted time he is obligated [to pay compensation].

• Bava Metzia 10:4

Answer 1

In the Mishna of BK, Ykar TYT said that the fall of the wall was unpredictable and the debris were in public domain, he did not make them Hefker and had time enough to clear the place and did not clear, his negligence caused the damage.

In the Mishna of BM, the same author said that in this case too the fall was unpredictable and the damage occurred or at the time of the fall, or quickly after the fall when the owner had not the time to clear the debris or in a case in which the owner did make Hefker and the debris are no more his mamon hamazik.

All this is in Gemara.

Answer 2

Whose translation is this? It seems to be a misleading one. This one's my own translation, but it's a much more literal one.

In the Mishnah in BK:

גדר שנפל לרה״ר והזיקו בהן אחרים חייב בנזיקן

A fence that fell into a public domain and others are damaged by them, he is obligated for their damage.

In that Mishnah it seems like it's discussing a case where the fence fell and others were damaged post-facto. It uses the terminology that "others" were damaged "by them" and not that it damaged, and it used a singular subject but a plural verb which clearly means that the "others" is in fact the subject, not the fence.

But in the BM Mishnah:

הכותל והאילן שנפלו לרה״ר והזיקו פטור מלשלם. נתנו לו זמן לקוץ את האילן ולסתור את הכותל ונפלו בתוך הזמן פטור. לאחר הזמן חייב.

A wall and a tree that fell into a public domain and they damaged, he is not obligated to pay. If [Beis Din] gave him time to cut down the tree and to knock down the wall but they fell within that time, he is not obligated. After that time, he is obligated.

In this case the verb is both of the same number as the subject and not in the context of others being damaged "by them". This time it seems to imply that the tree fell on somebody, not that someone tripped over it.

The distinction is clear. In the Mishnah in BK, it's discussing a case where it had already fallen even before someone was damaged. He's obligated because he needs to clean up his mess - it's equivalent to a pit (see BK 2b). In the Mishnah in BM, it hadn't fallen yet. In the first case, there was no way for him to be able to tell if it could harm. In the second case, although he still needed to take it down, he should have been able to leave it up to the end without it hurting anyone and thus he is still not obligated. Only in the last case was he negligent in not taking it down, and therefore he is liable when it falls on someone.