When does Apollo send a plague on the Greeks?

Apollo sends a plague on the Greeks during the Trojan War as a punishment for Agamemnon's disrespect towards his priest, Chryses, who sought the return of his daughter, Chryseis. Refusing to return her and insulting Chryses, Agamemnon incurs Apollo's wrath, leading the god to unleash a deadly plague upon the Greek camp. This event is depicted in Homer's "Iliad," highlighting the theme of divine retribution and the consequences of hubris.