Rashi on Genesis 49:9/רש"י על בראשית מ״ט:ט׳

1גור אריה A YOUNG LION — He prophesied this with reference to David who, when he began his military career, was but as a whelp — as it states, (2 Samuel 5:2) “when Saul was king over us it was thou that didst lead out and bring in Israel” — but who later on became as a lion when they made him king over themselves. That is what Onkelos means by translating it “A ruler he shall he בשרויא” — at the beginning

2מטרף FROM THE PREY (literally, tearing) — From the deed of which I suspected you when I said (Genesis 37:33) “Joseph is torn in pieces, an evil beast hath devoured him” — and by that Judah was meant who was likened to a lion —

3בני עלית THOU WENTEST UP, O MY SON — from that murderous deed you withdrew saying, (Genesis. 5:26) “what profit is it if we slay our brother”, and similarly did he act when Tamar was condemned to death, for he said “She is righteous: mine is the blame” (cf. Rashi on Genesis 38:26), therefore as a reward כרע רבץ HE STOOPED DOWN, HE CROUCHED etc. — as we are told of the days of Solomon (1 Kings 5:5) “[Israel dwelt safely] every man under his vine etc.” (Genesis Rabbah 99:8).