According to 911.gov you should call 911 in case of emergency (I quote) :
An emergency is any situation that requires immediate assistance from the police, fire department or ambulance. Examples include:
• A fire
• A crime, especially if in progress
• A car crash, especially if someone is injured
• A medical emergency, especially symptoms that require immediate medical attention
So I would say that tagging is not an emergency.
But...if you caught the guy, hit him with a baseball bat then you may be allowed to call 911 for medical support ;-)