The phrase "ratting on" is usually used to describe someone who informs on another person's actions or behaviors to authorities or other parties. Some possible antonyms for this phrase, then, might include "supporting," "defending," "covering for," or "standing by." For example, someone who is accused of a crime might hope that their friends or family members will "stand by" them and not "rat on" them to law enforcement. Similarly, in a workplace setting, colleagues who trust and respect each other might be more likely to "support" each other and avoid "ratting on" anyone for minor infractions or mistakes.