"If a man causes a field or vineyard to be grazed over" (Exodus 22:4): Why is this said? Before it is stated, one might say: I have it by logical argument. Since the pit is his property and the fire is his property, if you have learned that he is liable on account of his pit, shall he not be liable on account of the fire? And if I have established it by logic, what need is there for Scripture to say "if a man causes to be grazed over"? Rather, the verse comes to teach you that the tooth is a forewarned danger to eat what is fit for it, and the animal is a forewarned danger to break things in the manner of its walking. From here they said: a person is never liable until the damaging agent has gone out of his domain and caused damage. For damages are assessed from the best land, and all the more so concerning consecrated property.
Why Grazing Damage Needs Its Own Verse in the Torah
Yalkut Shimoni on Torah 344:1
(שמות כב ד) כִּי יַבְעֶר אִישׁ, לָמָּה נֶאֱמַר, עַד שֶׁלֹּא יֹאמַר, יֵשׁ לִי בְּדִין, הוֹאִיל וְהַבּוֹר מָמוֹנוֹ וְהַבְּעֵרָה מָמוֹנוֹ, אִם לָמַדְתָּ שֶׁיְּהֵא חַיָּב עַל יְדֵי בּוֹרוֹ, לֹא יְהֵא חַיָּב עַל יְדֵי הַבְּעֵרָה. אִם זָכִיתִי מִן הַדִּין, מַה תַּלְמוּד לוֹמַר כִּי יַבְעֶר אִישׁ, אֶלָּא בָּא הַכָּתוּב לְלַמֶּדְךָ שֶׁהַשֵּׁן מוּעָד לֶאֱכֹל הָרָאוּי לוֹ, וְהַבְּהֵמָה מוּעֶדֶת לִשְׁבֹּר בְּדֶרֶךְ הִלּוּכָה. מִכָּאן אָמְרוּ, לְעוֹלָם אֵינוֹ חַיָּב עַד שֶׁיָּצָא הַמַּזִּיק מֵרְשׁוּתוֹ וְהִזִּיק, שֶׁשָּׁמִין נְזָקִין בְּעִידִית וְקַל וָחֹמֶר לְהֶקְדֵּשׁ.