פירוש על בבא קמא 4:2

An ox that is accustomed for it's species is not accustomed...

הועד לקטנים – to calves.

An ox which is an attested danger for [injuring] its own kind, and is not an attested danger for [injuring] that which is not its own kind; or an attested danger for [injuring] human beings and not an attested danger for [injuring] beasts; or an attested danger for [injuring] children and not an attested danger for [injuring] adults that for which it is an attested danger [its owner] pays full damages, and that for which it is not an attested danger [its owner] pays half damages.
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.

We say that it was accustomed to 1 species but it's not accustomed to other species rather it is regarded as innocuous until it is accustomed. And as it says an ox that is accustomed to it's own species is not accustomed to a different species and thus the principle for all these halakos regarding an innocuous ox.

אמרו לפני ר' יהודה – his students asked of him.

And the words of R. Yehuda are correct.

Forewarned for Sabbaths – because he (i.e., the animal) is idle from work and it became overbearing; alternatively, because it sees human beings in their nice Shabbat clothing, they are considered in its eyes as known but he does not recognize them.

But he is not forewarned on weekdays, what is the law regarding this?

משיחזור בו שלשה שבתות – (see Tractate Bava Kamma, Chapter 2, Mishnah 4). After it (i.e., the owner of the ox) was forewarned for Sabbaths, they brought before him (i.e., the animal) oxen on three Sabbaths and it did not gore, it returned to its being innocuous, and if it returned to being innocuous and it gored, it (i.e., the owner) only pays one-half damages.