Rashi on Deuteronomy 25:11/רש"י על דברים כ״ה:י״א

1כי ינצו אנשים WHEN MEN STRIVE TOGETHER, they will in the end come to blows, as it goes on to state “[and the wife approacheth to deliver her husband]” out of the hand of him who smiteth him: No good can come out of a quarrel (Sifrei Devarim 292:1; cf. Rashi on v. 1).