QUESTIONS: The Mishnah (2a) lists four Avos Nezikin. The Gemara here records Rebbi Oshiya's Beraisa which lists thirteen Avos Nezikin. In addition to the four of the Mishnah, it adds the four types of Shomrim and the five payments ("Chamishah Devarim") that a person must pay when he does damage to another person. The Gemara explains that according to Rav, who maintains that "Mav'eh" in the Mishnah refers to Adam ha'Mazik (a person who does damage), the Mishnah includes in the word "Mav'eh" all of the additional Nezikin that Rebbi Oshiya mentions because they are all carried out by a person (Adam). Rebbi Oshiya, on the other hand, lists these Nezikin individually because Mav'eh refers only to Adam who damages a Shor (his friend's animal); the other five payments of an Adam who does damage are payments required of an Adam who damages another person.
RASHI explains that the proof that the Mishnah -- when it mentions Adam (Mav'eh) -- discusses only an Adam who damages a Shor (Nizkei Mamon) is that it lists Mav'eh together with Bor. The Mishnah refers only to a Bor that damages an animal, because one is not liable at all if his Bor damages a person (as the Gemara on 28b derives from Shemos 21:33). Similarly, it must be that the Mishnah discusses only Mav'eh that damages an animal (and not a person).
There are a number of questions on Rashi's explanation.
(a) Why does Rashi say that the Torah completely exempts a person when his Bor damages another person? The Gemara (28b, 53b; see also Rashi there) clearly says that the Torah exempts a person only when his Bor kills a person. If one's Bor damages a person, then he is obligated to pay for the damages. (TOSFOS RABEINU PERETZ; see RASHASH and Acharonim.)
If Rashi seeks to prove that the Mishnah is not discussing Avos Nezikin that killed a person, he should prove it from the case of Esh. One is exempt from payment when one's Esh kills a person because he receives a much more severe punishment ("Kam Lei bid'Rabah Minei"; see Rashi to 10a, DH Mah she'Ein Ken). Moreover, Rebbi Oshiya cannot be discussing a man who kills a man because he such a man would not be liable for "Chamishah Devarim." (See also TOSFOS to 5a, DH li'Me'utei, and MAHARAM SHIF here.) Obviously, Rashi is trying to show that the Mishnah is not even discussing damages done to a person. How, though, can he prove this from Bor, if one is liable for damages that his Bor does to a person?
TOSFOS RABEINU PERETZ suggests that Rashi means only that the main form of damage caused by a Bor which the Torah discusses is death, as the verse says, "v'Nafal Shamah Shor O Chamor" (Shemos 21:33). Therefore, the Mishnah is probably discussing a Bor that caused death, like the Bor of the verse. Hence, the Mishnah cannot be discussing a Bor that killed a person.
However, Rashi seems to exempt even the owner of a Bor even from damages done to a person, for he adds the word "[he is exempt] l'Gamri" -- "completely." Furthermore, if Rashi wants to prove with this logic that the Mishnah is not discussing a person who fell into a Bor, he should prove it from the fact that the Torah discusses an ox that falls into a Bor and thus the Mishnah also must be discussing an ox that falls into a Bor (regardless of whether or not the owner of the Bor is liable when a person falls into it).
(b) Why does Rashi not explain that the Gemara means simply that when Rebbi Oshiya lists Mav'eh, he obviously refers to a person who harmed a Shor as is clear from the fact that he lists, separately, a person who harms another person (by listing the five payments of "Chamishah Devarim"). Why is it necessary for Rashi to prove that the Mishnah cannot be referring to a person who damaged another person? Moreover, the Gemara earlier says that according to Rav, when the Tana of the Mishnah lists Mav'eh, he includes both a person who damaged an animal ("Adam she'Hizik Shor") and a person who damaged another person ("Adam she'Hizik Adam")! (TOSFOS RABEINU PERETZ)
(a) The Gemara (10a) writes that one is exempt when his Bor damages items that are not expected to be damaged by a Bor ("Davar she'Eino Ra'uy Lo"). Originally, the Gemara thought that this referred to Kelim, utensils, but the Gemara rejects this possibility and says that it refers to something else. It is not clear from the Gemara, however, what is considered something that is not fit for a Bor. RASHI (5b, DH v'Chulhu) writes that a "Davar she'Eino Ra'uy Lo" refers to a person.
TOSFOS there (DH Ki Shadis) is not satisfied with this explanation. Why should a person be considered unfit to be damaged by a Bor just because the Torah exempts the owner of the Bor from paying for the person's death? After all, the owner of the Bor is obligated to pay for damages that his Bor does to a person, and in that sense the person should be considered fit to be damaged by the Bor! Second, "Davar she'Eino Ra'uy Lo" does not mean an item for which the owner is not liable, but rather it means that this item is not normally damaged by such a Mazik. Why should a person be less fit than an ox to be damaged by a Bor?
The SHITAH MEKUBETZES cites RABEINU YISRAEL who explains that Rashi means that it is unusual for a person to fall into a Bor because a person usually looks where he is walking. That is the reason why the owner of the Bor is exempt if a person dies in his Bor; it was the person's fault for not being cautious. (See Gemara on 27b, "Iba'i Lei l'Iyunei.")
Later (9b), the Shitah Mekubetzes cites the GILYON who explains this more clearly. He writes that according to Rashi, the Torah exempts the owner of the Bor from responsibility for the death of a person because a person should watch where he walks. Nevertheless, the owner of the Bor is liable for damages done by his Bor to a person, since a person is cautious only to avoid an object that could cause his death; a person is not so careful to avoid something that will only damage him. Therefore, he does not notice the presence of a Bor that is less than ten Tefachim deep. (See also TORAH TEMIMAH, Shemos 21:263.)
However, according to this logic, the owner of a Bor that is ten Tefachim deep should be exempt even if a person falls in and is damaged, and not only if a person dies in it, because people avoid a Bor that can cause death! It seems, therefore, as the MESHECH CHOCHMAH (Shemos 21:33) points out, that according to Rashi the owner of the Bor would be liable for damages done to a person only when the Bor is less than ten Tefachim deep (and thus it can only cause damage and not death). If, however, the Bor is ten Tefachim deep, the owner of the Bor indeed would be exempt even from the damage that it causes to a person.
The Meshech Chochmah finds an allusion to this Halachah in the opinion of the Yerushalmi cited by the RASHBA (53b). The Yerushalmi rules that the owner of a Bor that is less than ten Tefachim deep is liable for damage done to Kelim (unlike the view of the Bavli). Only when the Bor is deeper than ten Tefachim is the owner exempt from paying for damage done to Kelim. (The Meshech Chochmah adds that when the depth of the Bor is ten Tefachim or more, people point it out to each other and caution each other to avoid it, since it could cause a person's death. When the Bor is less than ten Tefachim deep, a person might not notice it, and, moreover, people who do notice it will not make any effort to point it out to someone else walking near it.) (See also DEVAR MOSHE 78:2-8.)
This also explains what Rashi writes earlier (3a, DH v'Zeh Av l'Nezakin). Rashi there writes that when the verse says that "an ox... falls there (into the Bor)," it refers to both an ox that was damaged by a Bor and an ox that was killed by a Bor. TOSFOS (DH Lo) asks that if this is true, then when the word "Shor" teaches that one is liable only for damages done to an ox and not to a person ("'Shor' v'Lo Adam"), it should also exempt the owner of the Bor from paying for damage done to a person by his Bor, since the verse is discussing both damages and death. According to the way the Meshech Chochmah explains Rashi, this indeed is the Halachah. If a person falls into a Bor similar to the Bor of the verse (i.e. one whose depth is ten Tefachim or more) the owner of the Bor does not have to pay for damage done to the person. Only in the case of a Bor that is less than ten Tefachim deep must the owner pay for damages, and this is not the type of Bor that the Torah discusses.
Accordingly, this is what Rashi means when he writes here that the Bor of the Mishnah is exempt "l'Gamri," completely exempt from damages that it does to a person. He means that the Mishnah is discussing a ten-Tefach Bor, since that is the Bor to which the Torah refers. The owner of such a Bor is exempt from payment even when the Bor damages a person. This is also what the TALMID RABEINU PERETZ means when he writes that according to Rashi, the Mishnah is referring to the same Bor as the Torah, meaning a Bor that is at least ten Tefachim deep and which can cause death.
(b) Regarding the second question, why does Rashi need to prove that the Mishnah cannot be discussing a Bor that damaged a person, TOSFOS (DH Trei Gavni) asks why Rebbi Oshiya separates Adam into two groups ("Adam she'Hizik Adam" and "Adam she'Hizik Shor"), while he groups together Keren, Shen, and Regel all in one Av ("Shor" in the Mishnah, according to Rav). (See the answer of TOSFOS and MAHARAM.) Rashi may be bothered by this question as well. In order to answer this question, Rashi suggests that Rebbi Oshiya does not divide Shor into three separate categories, since the word "Shor" can include all three (Keren, Shen, and Regel). However, the word "Adam" in the Mishnah cannot include an Adam that damaged another Adam, as Rashi explains, and that is why Rebbi Oshiya found it necessary to add the list of obligations that are binding upon a person who damages another person.
Although Rav said earlier that when the Mishnah refers to Adam, it refers to all forms of damage caused by Adam, the Gemara now is retracting that answer and explaining that the Mishnah refers only to an Adam who damaged an animal according to Rav, and it omits the obligations that come from an Adam who damages an Adam, because the Mishnah is discussing only Avos Nezikin that cause damage to an animal and not to a person (as the Maharam explains).