A traffic officer was punched unconscious by a motorist he stopped.
The 35-year-old driver hit the officer several times in the face on Treforest Road in Stoke, Coventry during the early hours, police said.
The officer was knocked out for "a short amount of time" but got to his feet, chased and arrested the man, who had abandoned his car and fled.
The officer was treated by paramedics for facial injuries and was taken to hospital but later discharged.
"Despite being punched in the face and losing consciousness for a short amount of time, the officer still managed to chase and detain the suspect," police said.
The attacker was later found to be wanted by Derbyshire Police in connection with an armed robbery.
He remains in police custody and West Midlands Police said he will be spoken to in due course.