At around 7pm, police received a report of a stolen car in central Lien, 40 klilometres west of Oslo.
A few minutes later, the owner of the vehicle came face to face with the thief.
Aggrieved at the theft, he produced a spade and knocked his adversary unconscious with a blow to the head.
The injured man was taken to Ullevål hospital to be treated for his injuries.
The car owner was arrested and charged with assault causing bodily harm, according to police in the southern Buskerud district.