'Desertion' in the Bible

Then the commanders of [the] Philistines said, "What [are] these Hebrews [doing here]?" And Achish said to the commanders of [the] Philistines, "Is this not David, the servant of Saul, the king of Israel, who has been with me {for days and years}? I have not found anything [threatening] in him from the day of his desertion until this day!"