The LORD was with him: see the comments on 16.18. The context clearly shows that David is the antecedent of the pronoun him (see also 16.13-14, where it is said that God’s spirit was with David but departed from Saul).

In some languages this verse will sound more natural if restructured to indicate the reason for Saul’s fear before stating the fact. A possible model is “The LORD was with David, but he was no longer with Saul. Therefore, Saul was afraid of David.”

Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 1. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .