1 Samuel 20:30
Then Saul’s anger was kindled against Jonathan, and he said unto him, Thou son of the perverse rebellious woman, do not I know that thou hast chosen the son of Jesse to thine own confusion, and unto the confusion of thy mother’s nakedness?
This outburst belongs to the history after the slaying of Goliath, when Saul kept David with him and would not let him return to his father's house. By that time the soul of Jonathan was knit with the soul of David, and Jonathan loved him as his own soul. They made a covenant to be united as brethren, and in token of it Jonathan gave David his robe and his garments, even his sword and his bow and his girdle.
That union was a most sacred bond that remained unbroken until the deaths of Saul and Jonathan. It was the Lord's doing, so that Jonathan might be the means of preserving David's life when Saul would try to kill him. The immediate trigger for Saul's words in this verse was Jonathan telling him that David had gone to Bethlehem for his family's sacrifice, at which Saul's anger became ungovernable.
Saul was angry at Jonathan for supporting David, declaring that as long as the son of Jesse lived Jonathan could not come to the throne of Israel. He demanded that David be sent for immediately to be put to death. When Jonathan interceded for David by asking why he should be killed and what he had done, Saul grew more furious.
In that fury he hurled at his own son the spear he had intended for David. The outburst settled that David must flee, and its dark shadow fell upon both young men. So Jonathan left the feast grieved and indignant to warn David. Saul's words in this way expose the loss of his own rule and the end of his family's royal hopes, a fate he repeatedly foretold because of his sins.