Final answer:
Billy utilized displacement as a defense mechanism by redirecting his anger from his coach to his stuffed animals at home.
Step-by-step explanation:
Billy displayed the defense mechanism known as displacement. Displacement is a psychological defense mechanism where a person redirects a negative emotion from its original source to a safer or more convenient target. In this scenario, Billy did not express his anger towards his coach, which would have been socially inappropriate or might have had negative consequences. Instead, he transferred his anger onto an inanimate object, his stuffed animals, upon reaching a more private setting like his home.