Rashi on Deuteronomy 33:20/רש"י על דברים ל״ג:כ׳

1ברוך מרחיב גד BLESSED BE HE THAT ENLARGES GAD — this teaches us that Gad’s territory extended far eastward (Sifrei Devarim 355:2).

2כלביא שכן HE DWELLETH AS A LIONESS — Because he was near the border it therefore compares him to lions, for all who are near the border must be strong (that they may repulse attacks from neighbours) (Sifrei Devarim 355:3).

3וטרף זרוע אף קדקד TEARING THE ARM WITH THE CROWN OF THE HEAD — Those whom they slew could be easily recognised, because they used to cut off the head together with the arm at one blow.