Policeman negligence question?

Can a policeman be responsible for a car accident caused by someone he was chasing if the chase was not worth the consequence of the chase (the person being chased hitting the victim)? For example, if a police officer pulls over someone for a minor road infraction such as an illegal turn, and the person speeds off and provokes a chase and eventually hits someone, is the officer ever liable for adding to the chase for a small infraction that would not warrant such a chase, or is being a police officer always a complete defense?