He did put his life in his hand, i.e. he exposed his life to eminent hazard. See Poole on "Judges 12:3".
Related Commentaries of 1 Samuel 19:5
1 Samuel 19:5
5 For he did put his life in his hand, and slew the Philistine, and the LORD wrought a great salvation for all Israel: thou sawest it, and didst rejoice: wherefore then wilt thou sin against innocent blood, to slay David without a cause?