The phrase "sit on the fence" refers to someone who is indecisive about a particular issue or situation. Antonyms for this phrase would include someone who is decisive, confident, or resolute. These individuals take a clear stand on their beliefs and do not waver in their opinions. They may be considered assertive, determined, or steadfast. Antonyms for "sit on the fence" could also include words such as committed, resolved, and unwavering. These individuals have a strong sense of conviction about their values and ideas, and are willing to take action to support them.