Albert Barnes Commentary 2 Samuel 23:14

"And David was then in the stronghold; and the garrison of the Philistines was then in Beth-lehem." — 2 Samuel 23:14 (ASV)

In a hold — This refers to the hold mentioned in 1 Chronicles 11:16, which was near the cave of Adullam (according to a marginal note). It shows the power and daring of the Philistines that they held a post as far into the country as Bethlehem.