Authorities say another driver called police in Fairfield Saturday night to report that the man was driving erratically and appeared to be drunk.
According to police, the concerned driver approached the pickup truck and tried to remove the keys.
As officers arrived, police say the pickup truck driver put the truck in gear and rammed a Fairfield marked police car, then backed up and drove over a median in the direction of a police officer.
Authorities say the officer had no escape and fired his gun, striking the suspect in the head.
The 46-year old suspect was taken to St. Joseph Hospital in Paterson, where he is in critical but stable condition, and has been placed under arrest.
The Fairfield officer is a 10-year veteran who was taken to a hospital and evaluated.