Final answer:
Valarius uses the fall of a brazen shield, which emits a loud ringing sound, to distract Radulf and prevent him from killing Nic.
Step-by-step explanation:
Valarius distracts Radulf from killing Nic in the arena by using a clever tactic involving a brazen shield. As the champion who faced the dragon, Valarius moves the dragon's carcass aside and advances toward the shield. Upon reaching the shield, it does not wait for him to touch it, but rather it falls to the floor, making a mighty great and terrible ringing sound. This loud, unexpected noise is what distracts Radulf, saving Nic from his impending doom. The enchantment tied to the shield is broken with the shield's fall, thus shifting the focus from Nic and creating a moment of respite for him in the arena.