Albert Barnes Commentary 2 Samuel 5:17

"And when the Philistines heard that they had anointed David king over Israel, all the Philistines went up to seek David; and David heard of it, and went down to the stronghold." — 2 Samuel 5:17 (ASV)

The hold - Not the same place named in 2 Samuel 5:7, 9, but probably the cave (or hold) of Adullam (2 Samuel 23:13). The invasion most likely took place before David had completed his buildings in the city of David and is probably the one referred to in 2 Samuel 23:8–17.