Saul was upset that his son Jonathan had acted in David’s best interests.1 The fact that he accused Jonathan of siding with David also suggests that he considered Jonathan’s actions to be a clear demonstration of his allegiance.2 Instead of being loyal to Saul and his family, Jonathan was loyal to David.
30 Then Saul’s anger was kindled against Jonathan, and he said to him, “You son of a perverse, rebellious woman, do I not know that you have chosen the son of Jesse to your own shame, and to the shame of your mother’s nakedness?