THE ATHEIST'S COMPLAINT:
Who killed Goliath? Did David kill him twice, once with a sling and once with a sword (1 Samuel 17:49-50, 51; 21:8-9) or did Elhanan (2 Samuel 21:19) [NOTE, the words 'the brother of' were inserted by the KJV translators to avoid the obvious contradiction with 1 Samuel 17:49-51]? Is there a contradiction?

RESPONSE:
First let us address the question of whether it was David or Elhanan who killed Goliath, then we shall address the manner in which the giant died.

I am curious why, but not surprised that, the questioner did not mention 1 Chronicles 20:5, which is a parallel text to 2 Samuel 21:19. 1 Chronicles 20:5 reads, "And there was war again with the Philistines; and Elhanan the son of Jair slew Lahmi the brother of Goliath the Gittite, whose spear staff was like a weaver's beam." It is evident from this text that Elhanan killed Goliath's brother, not Goliath. It is true that the words 'the brother of' do not appear in available Hebrew text of 2 Samuel 21:19. Adam Clarke's Commentary states, "The corruption may be easily accounted for by considering that oregim, which signifies weavers, has slipped out of one line into the other; and that beith hallachmi, the Beth-lehemite, is corrupted from eth Lachmi; then the reading will be the same as in Chronicles."

David and Elhanan killed two different men. David slew Goliath, the mighty champion of the Philistines. Elhanan slew Lahmi, the brother of Goliath.

There is no contradiction.

This article is a response to Skeptic's Annotated Bible.
NOTE, what David killed Goliath with is dealt with in the April 30, 2006 ATA article

---