Rashi on Exodus 22:4/רש"י על שמות כ״ב:ד׳

1כי יבער … בעירה ובער All these terms are connected with the word בעיר which signifies “cattle”, as in (Numbers 20:4) אנחנו ובעירנו “we and our cattle" .

2כי יבער means accordingly, he takes his cattle into the field or the vineyard of his fellow-man and causes damage to him by one of these two ways: either by the mere fact that he lets his cattle go (tread) there (ושלח את בעירו), or by letting it graze there (ובער). Our Rabbis explained (Bava Kamma 2b), that ושלח refers to the damage done by “treading” (Rashi uses a Biblical phrase Deuteronomy 5:1. “treading of the hollow of the foot”) and ובער to the damage caused by the tooth that eats up and removes (מבערת) the crops (grazing).

3בשדה אחר means בשדה של אחר IN THE FIELD OF ANOTHER MAN (not “in another field”, when it would be punctuated בְּשָׂדֶה, for בִּשְׁדֵה is the construct form).

4מיטב שדהו … ישלם THE BEST OF HIS FIELD SHALL HE PAY — We assess the damage, and if the defendant proposes to make restitution to him for the damage he has suffered with “land’” then he has to pay him with the best of his fields. If for instance the damage amounted to a Sela he has to give him a Sela-worth of the best of the fields he possesses). Scripture teaches you that in cases of damages (which it is proposed to pay with land) we assess and collect them from the best land of the defendant (Mekhilta; Bava Kamma 6b).