Contradiction with 2 Samuel 21:19
This verse claims Elhanan killed Goliath, contradicting the account in 1 Samuel 17:21 where David is preparing to fight Goliath.
2 Samuel 21:19: And there was again a battle in Gob with the Philistines, where Elhanan the son of Jaareoregim, a Bethlehemite, slew [the brother of] Goliath the Gittite, the staff of whose spear [was] like a weaver's beam. [Jaareoregim: or, Jair]
Contradiction with 1 Samuel 16:14-23
This passage suggests David was already serving Saul before the battle with Goliath, conflicting with 1 Samuel 17 where Saul seems not to know David.
1 Samuel 16:14-23: But the Spirit of the LORD departed from Saul, and an evil spirit from the LORD troubled him. [troubled: or, terrified]
Contradiction with 1 Samuel 17:55-58
Saul does not recognize David after he defeats Goliath, which contradicts the previous relationship described in earlier chapters where David played the harp for him.
1 Samuel 17:55-58: And when Saul saw David go forth against the Philistine, he said unto Abner, the captain of the host, Abner, whose son [is] this youth? And Abner said, [As] thy soul liveth, O king, I cannot tell.
Contradiction with 1 Chronicles 20:5
Similar to 2 Samuel 21:19, it states that Elhanan killed Lahmi, the brother of Goliath, introducing further confusion about who killed whom.
1 Chronicles 20:5: 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. [Jair: also called, Jaareoregim]