What did Saul hurl at David while David played the harp?

Answer: A spear

Jealous Saul tried to pin David to the wall with his spear (KJV: javelin), but David eluded him.

“The next day a spirit of distress sent from God came upon Saul, and he prophesied inside the house while David played the harp as usual. Now Saul was holding a spear,”— 1 Samuel 18:10 (BSB)