Wicked in the sight of the Lord, i.e. notoriously wicked. Compare Genesis 10:9, Genesis 13:13. The Lord slew him, in some extraordinary and remarkable manner, as Genesis 38:10.
Related Commentaries of Genesis 38:7
Genesis 38:7
7 And Er, Judah's firstborn, was wicked in the sight of the LORD; and the LORD slew him.