An Ambulance Chaser is a term for an unethical lawyer, especially those who represent plaintiffs in personal injury actions.
The term is derived from lawyers who follow ambulances to hospitals after a person is injured, usually determined through the lawyer's use of a personal police/fire radio scanner, in order to attempt to drum up business by convincing a victim that he or she needs to sue, or by simply being the first lawyer in contact with the victim, generally when the victim is most prone to suggestion and easily talked into suing.
In most jurisdictions, lawyers can be disbarred if caught engaging in such unethical behavior. Bar associations regularly dispatch investigators to large-scale disaster scenes to look out for unethical lawyers or their non-lawyer agents (known as "cappers" or "runners").
Good Example of Ambulance Chaser:
A lawyer who comes to a classroom and asks the students who were bullied to sue the bully for intentional infliction of emotional distress, so he in turn can receive a large contingency fee.