Nevertheless Saul didn't say anything that day: for he thought, Something has happened to him. He is not clean. Surely he is not clean.
Saul had, at this time, become very suspicious and critical of his son Jonathan, especially regarding his friendship for David.  One may wonder if some tattle tale at Saul's court, who perhaps had seen David and Jonathan together "in the field," had told Saul of it.  At any rate, Saul demanded from Jonathan a reason for David's absence.