Contradiction with 2 Samuel 1:14
It contradicts 2 Samuel 1:8 by showing David's belief that it is wrong to harm the anointed of the Lord, yet in 2 Samuel 1:8, the young man admits to killing Saul, the anointed king.
2 Samuel 1:14: And David said unto him, How wast thou not afraid to stretch forth thine hand to destroy the LORD'S anointed?
Contradiction with 1 Samuel 31:4
It contradicts 2 Samuel 1:8 by suggesting that Saul died by his own sword, whereas 2 Samuel 1:8 is part of a claim that the Amalekite took credit for killing Saul.
1 Samuel 31:4: Then said Saul unto his armourbearer, Draw thy sword, and thrust me through therewith; lest these uncircumcised come and thrust me through, and abuse me. But his armourbearer would not; for he was sore afraid. Therefore Saul took a sword, and fell upon it. [abuse...: or, mock me]