An arrest requires physical restraint or submission to an officer's show of force. Police need "probable cause" in order to make a lawful arrest.
Whether a person is "under arrest" depends on the circumstances of the police encounter.
When the Police Can Make an Arrest: Probable Cause
"Probable cause" requires more than a mere suspicion that a suspect committed a crime, but not as much information as would be required to prove a suspect guilty beyond a reasonable doubt.
Historically, American citizens were legally entitled to use reasonable force to resist unlawful arrest. Some states continue to follow this rule, while others don’t.
Timely Arrest: How Long the Police Have to Arrest Someone
Police officers are generally free to determine when to arrest someone; they need freedom to investigate the crime and collect evidence.
How much "probable cause" do the police need?
“Probable cause” is the standard by which judges evaluate many police actions.
What Is a Probable Cause Hearing?
"Probable cause hearing” typically refers to a quicker proceeding involving a determination that there was a valid basis for arrest.
Can I be charged with a crime without being arrested?
Citations are increasingly being used, as jail space gets scarce.
Does an Officer Have to Witness a Misdemeanor in Order to Make an Arrest for It?
In most states, the misdemeanor must occur in the officer's presence.