"Throwing in with" is a colloquial phrase that means to join forces with someone or align oneself with a group. Its antonyms vary depending on the specific context in which the phrase is used. For example, if "throwing in with" is used to describe joining a team or becoming part of a group, the antonym could be departing or leaving the team, or simply not aligning oneself with the group. If the phrase refers to supporting a decision or action, some antonyms could be resisting, opposing or dissenting from it. Overall, the antonyms for "throwing in with" depend on the specific context and circumstances, but they generally involve notions of separation or doing the opposite.