Commentary for Bava Kamma 4:2
שׁוֹר שֶׁהוּא מוּעָד לְמִינוֹ וְאֵינוֹ מוּעָד לְשֶׁאֵינוֹ מִינוֹ, מוּעָד לְאָדָם וְאֵינוֹ מוּעָד לִבְהֵמָה, מוּעָד לִקְטַנִּים וְאֵינוֹ מוּעָד לִגְדוֹלִים, אֶת שֶׁהוּא מוּעָד לוֹ מְשַׁלֵּם נֶזֶק שָׁלֵם, וְאֶת שֶׁאֵינוֹ מוּעָד לוֹ מְשַׁלֵּם חֲצִי נֶזֶק. אָמְרוּ לִפְנֵי רַבִּי יְהוּדָה, הֲרֵי שֶׁהָיָה מוּעָד לְשַׁבָּתוֹת וְאֵינוֹ מוּעָד לְחֹל. אָמַר לָהֶם, לַשַּׁבָּתוֹת מְשַׁלֵּם נֶזֶק שָׁלֵם, לִימוֹת הַחֹל מְשַׁלֵּם חֲצִי נֶזֶק. אֵימָתַי הוּא תָם. מִשֶּׁיַּחֲזֹר בּוֹ שְׁלשָׁה יְמֵי שַׁבָּתוֹת:
If an ox were a muad to (animals of) its kind, and not a muad to (animals) not of its kind; a muad to men, and not a muad to beasts; a muad to small (animals) [i.e., calves], and not a muad to large — for what it is a muad to, it pays a full nezek, and for what it is not a muad to, it pays a half-nezek. They [his disciples] asked R. Yehudah: What [is the halachah] if it were a muad for Sabbaths but not for weekdays? [("a muad for Sabbaths":) Because it does not work then and its "mind" has free rein; or else, because it sees men in Sabbath finery, they appear strange to him, and he does not recognize them.] He answered: For Sabbaths, it pays a full nezek, and for weekdays, a half-nezek. When does he become a tam (again)? After desisting on three Sabbaths. [If, after being (confirmed as) a muad for Sabbaths, they pass before him oxen on three Sabbaths and he does not gore them, he reverts to his status of tam, after which, if he gores again, he pays only a half-nezek.]
Rambam on Mishnah Bava Kamma
Bartenura on Mishnah Bava Kamma
English Explanation of Mishnah Bava Kamma
They said in front of Rabbi Judah: “What if it is an attested danger on the Sabbath, and it is not an attested danger during the week?” He said to them: “For [injuries done on] Sabbaths [its owner] pays full damages and for [injuries done] during the week [its owner] pays half damages.” When will this ox be considered harmless? After it refrains from doing injury for three Sabbath days.
Our mishnah continues to discuss the meaning of the concepts of muad, an ox which is an attested danger, and tam, an ox which is considered harmless. We have already mentioned many times that a muad is an ox that has already injured three times (see chapter 2 mishnah 4). If it should damage again it’s owner will be obligated for full damages, and not half damages as is obligated the owner of a tam. Our current mishnah will clarify that an ox (or any animal) can be considered a muad for some types of injury and a tam for others.
The first section of the mishnah deals with an ox that is known to damage certain types of animals or people but not others. For instance it is known to damage other oxen, but not sheep, or people but not animals, or children but not adults. In each of these cases the ox can be treated as a muad for specific things but a tam for others. The reasoning is that since it is known to injure, for example children, its owner must be extra careful around children. However, around adults, the owner can be less concerned and therefore he will only be liable for half damages.
The second section of the mishnah discusses the idea that an ox might be known to damage on certain days. This is a somewhat more perplexing idea. After all, it seems logical that an ox might become more testy around other oxen and be less bothered by sheep. Section one’s distinctions are therefore logical. However, one might not imagine that an ox is smart enough to know the difference between days of the week. Nevertheless, Rabbi Judah concludes that if we have evidence that an ox is more likely to attack on the Sabbath it could become a muad just for that day. At the end of the mishnah we learn that in order for this ox to revert to tam status, it would have to refrain specifically from its muad behavior. Therefore a muad for the Sabbath would have to refrain from injuring on the Sabbath itself, and not just during the week.