Out rival means to defeat or surpass someone in a competition or achievement. Some antonyms for out rival could be 'underperform', 'fall behind', 'lose', 'subordinate', 'inferior', or 'lag'. These words are the complete opposite of out rival as they convey the losing or low achieving aspect of a situation. These words can be used in contrast to out rival, which denotes the concept of outperforming and being on top of a situation. Hence, depending on the context, the antonyms of out rival can be used to describe a situation where someone is not able to achieve as much as others or they are unable to surpass their competitors.