1. was destroyed by THANOS
In Infinity Gauntlet battle, the captain fights with Thanos, but with a degree of power. Just his only scary attack. The captain's shield has become a scrap. This scene is likely that we may see in the Avenger Infinity War to be released next year, it is possible.
2. Thor smash by Mjolnir
Thor gains the power of Odin Force, giving him the power of gods, but Thor's attacks are not so great, so the captain's shield is broken. Just his shield is only dented. After the fight has ended Thor uses his own hammer to repair the shield back to its original state.
3. The Moleculeman's destroyed Shield.
He can control all kinds of molecules, whether living or dead. And everything is composed of molecules. In addition to the Captain's shield, Thor's Mjolnir hammer was also destroyed, but after the Moleculeman's maneuver, he used his own powers to build a new Captain's shield.
4. The shield is cancer.
Can the shield have cancer? After the Moleculeman's destroyed the shield of the captain then. He created a shield for the captain once again with the power of a molecule. However, he has misplaced the molecule, causing the shield to break apart.
5. Doctor Doom destroyed Shield.
Once a captain has fought with Doctor Doom, he can twist the shield of the captain. But after the battle ends, everyone can ask for a blessing and the captain asks for his shield to return to normal.