Matthew Poole and continuators on 1 Samuel 18:13

13 Therefore Saul removed him from him , and made him his captain over a thousand, and he went out, and came in before the people.

From his Presence and Court; which he did, partly, because he feared lest David should watch and find an opportunity to kill him, as he had designed to kill David; partly, because he was a great Eye-sore, and his presence now made him more sad than ever his Musick had made him chearful: and principally, that hereby he might expose him to the greatest hazards, and in some sort betray him into the hands of the Philistines.

He led his Soldiers forth to Battel, and brought them back again with safety. Compare 2 Sam. 5. 2. Or else the Phrase of coming in and going out, may be understood (as elsewhere) for conversing; or (as we use to say) going to and fro about business; as chap. 29. 6.