Antonyms for the phrase "are on a team" are primarily those that refer to a lack of collaboration, communication, or cooperation. Some antonyms include working solo, going it alone, individualistic, uncooperative, competitive, and standoffish. People who are not on a team tend to do things on their own, without considering how their actions may impact others. They may be less likely to communicate clearly or work together to achieve a common goal. In contrast, being on a team requires individuals to put aside their personal objectives and work together to achieve a shared goal. Effective teamwork is essential for success in almost every field, including sports, business, and politics.