The phrase "be losing" can be described in several ways using synonyms. One could say that they are "falling behind" in a competition or game. They may also be "slipping" or "lagging" in performance. Additionally, they could be "trailing" or "faltering" in progress. In a more negative sense, they could be "suffering a defeat" or "coming up short". Alternatively, they may simply be "not winning" or "not ahead". No matter the choice of words, the underlying meaning is the same: the individual or team in question is not currently in the lead or performing at their best.