Jamieson, Fausset and Brown on 1 Chronicles 11:23

23. he went down--the ordinary phraseology for expressing an engagement in battle. The encounter of Benaiah with this gigantic Egyptian reminds us, in some respects, of David's combat with Goliath. At least, the height of this giant, which was about eight feet, and his armor, resembled his of Gath.

with a staff--that is, having no other weapon in his hand than his walking stick.