When it comes to stopping something from happening, it's important to act quickly and efficiently. Some synonyms for the phrase "immediately intervene to stop" would include "swiftly intercede," "promptly obstruct," and "instantly halt." Other options could include "abruptly interrupt," "directly interject," or "urgently interfere." Whatever word choice you use, the message remains clear: it's crucial to take action as soon as possible in order to prevent a negative outcome. By using impactful language, you can convey a sense of urgency and highlight the importance of immediate action.