When you "go up against" someone or something, you are facing a challenge or opposition. In order to express this idea in different words, there are several synonyms that can be used. For instance, you can say "compete with," "confront," "battle," or "face off against" instead of "go up against." These alternatives convey similar meaning in terms of the confrontation or competition involved, but they add different nuances to the situation depending on the context. Regardless of which term is used, each synonym implies a level of intensity and struggle in the situation where someone is facing off against an opponent or obstacle.