It is unlikely that Saul would have forgotten Samuel’s and God’s rejection of him as king, so when David started having success in everything, this insecure king had good reason to be worried. Saul is recorded as becoming jealous, which left the (spiritual) door open for an evil spirit to move in on Saul, leading him to make multiple attempts on David’s life.
David escaped, of course, and his prayer shows his concerns about his would-be assassins, but nevertheless found his safety in God. He had an interesting view of how his enemies (those wanting to kill him) should be dealt with:
Psalm 59:11 Don’t kill them, for my people soon forget such lessons; stagger them with your power, and bring them to their knees, O Lord our shield.
That prayer was answered when Saul’s men started prophesying as they attempted to capture David. Then Saul made an attempt, and he ended up lying naked on the ground and prophesying all day and night.
That Bible blog 