The phrase "catch in the act" typically refers to catching someone in the midst of doing something wrong, illegal or shameful. The antonyms for "catch in the act" could range from catching someone in the act of doing something positive or commendable, such as performing an act of kindness, to catching someone doing nothing at all. Other antonyms could include catching someone after the fact, when they have already completed the action in question and cannot be apprehended, or catching someone in the act of being honest and forthright. Ultimately, there are many different antonyms for "catch in the act" depending on the context and circumstances in which the phrase is used.