was wicked in the sight of Yahweh

The phrase "in the sight" refers to Yahweh seeing Er's wickedness. AT: "was wicked and Yahweh saw it" (See: rc://en/ta/man/translate/figs-idiom)

Yahweh killed him

Yahweh killed him because he was wicked. This can be made clear. AT: "So Yahweh killed him" (See: rc://en/ta/man/translate/figs-explicit)