The priest said, The sword of Goliath the Philistine, whom you killed in the valley of Elah, behold, it is here wrapped in a cloth behind the ephod: if you will take that, take it; for there is no other except that here. David said, There is none like that; give it me.
Now it does definitely declare that David was afraid of Achish. The fear of man can oftentimes cause a person to act like a fool. It brings a snare. So my brave David, he's not afraid of the giant, he's afraid of the king. So acting like a madman, he's reduced to a man with spit running down his beard and scrabbling on the doors and gates, but he did escape out of the hand of Achish. "