Final answer:
A police officer can take legal action without a warrant if there is probable cause, such as making an arrest for a felony crime or witnessing a minor crime or misdemeanor.
Step-by-step explanation:
When a police officer doesn't have a warrant, there are certain legal actions they can take. One such action is conducting an arrest if there is probable cause to believe a felony has been committed. Additionally, police can arrest someone for minor crimes or misdemeanors they witnessed themselves. However, it's important to note that these actions must still adhere to the requirements of probable cause.