Read 1 Chronicles 12:19 Using Other Translations
And there fell some of Manasseh to David, when he came with the Philistines against Saul to battle: but they helped them not: for the lords of the Philistines upon advisement sent him away, saying, He will fall to his master Saul to the jeopardy of our heads.
Some of the men of Manasseh deserted to David when he came with the Philistines for the battle against Saul. (Yet he did not help them, for the rulers of the Philistines took counsel and sent him away, saying, "At peril to our heads he will desert to his master Saul.")
Some men from Manasseh defected from the Israelite army and joined David when he set out with the Philistines to fight against Saul. But as it turned out, the Philistine rulers refused to let David and his men go with them. After much discussion, they sent them back, for they said, “It will cost us our heads if David switches loyalties to Saul and turns against us.”