When they defied the Philistines that were there gathered - This is supposed to refer to the war in which David slew Goliath.
Gone away - Rather, went up to battle (2 Samuel 5:19; 2 Kings 3:21, etc.) against them. These words and what follows as far as “troop” 2 Samuel 23:11 have fallen out of the text in Chronicles. The effect of this is to omit EIeazar‘s feat, as here described, to attribute to him Shammah‘s victory, to misplace the flight of the Israelites, and to omit Shammah altogether from the list of David‘s mighty men.