(Mishnah): What is the law of an ox that damaged in the victim's premises?

If it gored, pushed, bit, crouched or kicked in Reshus ha'Rabim, it pays half-damage;

In the victim's premises, R. Tarfon obligates full damage;

Chachamim say, it pays half-damage.

R. Tarfon (to Chachamim): In a place where the Torah is lenient to exempt Shen and Regel, i.e. in Reshus ha'Rabim they are exempt, it is stringent about them in the victim's Reshus, to pay full damage. In a place where it is stringent about Keren, to pay half-damage in a Reshus ha'Rabim, all the more we should be stringent about them to pay full damage in the victim's premises!

Chachamim: Dayo (it suffices) to learn from a Kal va'Chomer to be like the source (we cannot learn more than the source). Just like [Keren] pays half-damage in a Reshus ha'Rabim, also in the victim's premises it pays half damage.

R. Tarfon: I will not learn Keren from Keren. I will learn Keren from Regel!

In a place where the Torah is lenient [to exempt] Shen and Regel, in Reshus ha'Rabim, it is stringent about Keren. In a place where it is stringent about [Shen and Regel], in the victim's Reshus, all the more so we should be stringent about Keren [to pay full damage]!

Chachamim: Dayo to learn from a Kal va'Chomer to be like the source. Just like in Reshus ha'Rabim [Keren] pays only half-damage, also in the victim's Reshus, half-damage.

(Gemara - R. Yochanan): [The Mishnah] is like R. Tarfon. In the victim's Reshus, R. Tarfon says that [a Tam] pays full damage. Chachamim say, it pays half-damage.

Note: R. Yochanan said so about Mishnah 1:4, which calls an ox that damages in the victim's premises 'Mu'ad'. His words were copied and put on our Mishnah, even though they are not appropriate here. The Yerushalmi often does so.