Abandoning one's country or side in a war to join the other side (or to at least seek asylum on the other side).
Key passages
2 Sa 3:9–10

Thus may God punish Abner, if I do not accomplish what Yahweh has sworn to David; specifically, to transfer the kingdom from the house of Saul and to establish the throne of David over Israel and over Judah from Dan to Beersheba!”

1 Ch 12:8–15

And from the Gadites, valiant mighty warriors, soldiers fit for war, expert with shield and spear, defected to David at the fortress toward the wilderness. And they had faces like lions and were swift as gazelles upon the mountains. Ezer the chief, Obadiah second, Eliab third, Mishmannah …

1 Ch 12:19–22

And some Manassites deserted to David when he came with the Philistines to the battle against Saul, but he did not help them, for the rulers of the Philistines sent him away upon counsel, saying, “He will desert to his master Saul at the cost of our heads.” When he went to Ziklag some Manassites …