Sentence examples for on case from inspiring English sources

No, the phrase "on case" is not a complete thought and is not grammatically correct in English.
It is possible that you are thinking of the phrase "in case," which is a common phrase meaning "in the event that" or "just in case." For example: I brought an umbrella in case it rains. Can you please leave your phone on in case I need to reach you? In case of emergency, please call 911. If you are referring to the word "on" as part of a preposition (e.g. "on the case"), then it would be grammatically correct and can be used in written English. However, it would depend on the context and meaning you are trying to convey. Here are some examples: The police are on the case and are actively investigating the crime. I'm glad you're on the case, your expertise will be valuable in solving this problem. She's always on the case and never lets anything slip by unnoticed.