The sign of Eli's curse came to fruition (both his sons died) and the ark of God was captured
Israel encamped at Ebenezer and the Philistines encamped at Aphek for battle. Israel was defeated, losing 4000 men. They brought out the ark of the covenant to the camp with Hophni and Phinehas. They shouted, scaring the Philistines who thought the gods that struck the Egyptians had come into their came, so they told each other to take courage and be men. Israel lost greatly, losing 30,000 men, the ark of God, and Hophni and Phinehas's lives. (1 Samuel 4)
David was disallowed to participate in a battle against Israel and sent home from Aphek
The Philistines gathered all their forces at Aphek, by hundreds and thousands, while the Israelites were encamped by the spring in Jezreel. The lords of the Philistines asked why these Hebrews were here, and despite Achish insisting David's blamelessness to their cause, he had to send David back to Philistia early next morning, while the Philistines continued to Jezreel. (1 Samuel 29)