Or HaChaim on Exodus 21:35/אור החיים על שמות כ״א:ל״ה

1 שור איש את שור רעהו, one man's ox that of another, etc. The reason the Torah writes the word את is because the scenario we deal with assumes A) that there were no witnesses, B) that both oxen are of equal value while alive; if, however, the attacking ox was clearly more valuable than its counterpart, the owner of the victimised ox is entitled to only half the value of the damage he has sustained; this is the ruling given in Baba Kama 34. The Talmud writes as follows: "If the value of the offending ox is less than that of the victim, we do not allow the owner of the victim to receive more than half the value of the offending animal. If we were to allow that, then the Torah should not have made the compensation depend on the sale of the surviving ox and its proceeds, but the Torah should have written: 'he shall pay him half the damage he has sustained.' The wording of the Torah proves that the owner of the dead ox does not receive more than half the value of the surviving ox even if this amounts to less than half the amount of damage he has sustained." The Talmud did not bother to mention that the owner of the victimised ox will certainly not receive more than half the value he has sustained. If we were to assume that the Torah assigns half of the value of the surviving animal to the owner of the victimised animal, it could happen that if the surviving animal is worth more than twice the value of the animal killed, the owner of the dead ox would receive more than the total value of the dead animal (while it was alive) as compensation. Such a situation is obviously not intended by the Torah.