Legal Question in Civil Litigation in California

Anyone can be called as a witness who shows up in court. There may be local rule limitations on it, however, if you were not on the defendant's witness list. In most courts, however, the defense can call anyone on the plaintiff's list, although if the plaintiff releases you from the subpoena you don't have to show. So I always issue my own subpoena for witnesses I want to call, rather than risk the plaintiff calling up the witness and withdrawing the subpoena on the eve of trial.

If you're present in court, you can be called to testify.