The phrase "was on one's side" generally connotes support or favor. The antonymic phrases for this expression could be "was against one," meaning hostility or opposition, or "was impartial," suggesting neutrality or lack of bias. When someone is against you, they work in opposition to you, whether it is socially, emotionally, or politically. Similarly, if someone is impartial, they are neutral and do not take any active part in your affairs. Therefore, context plays a significant role in determining the antonyms for the phrase "was on one's side.
