A teenager was injured when he tried to stop a thief stealing his mother's car from their driveway in Worcestershire.
The boy's mother had left the engine running as she went back into the house in Pinewoods Avenue, Hagley, at 0815 GMT, police said.
The teenager saw a man reverse the black Renault Laguna, registration DX07 FUH, out of the drive. The boy hurt his hand and shoulder when he slipped.
Two other cars in the area were also stolen when they were left to warm up.
In the incident in Pinewoods Avenue, the stolen car was followed by a silver Ford Mondeo.
Pc Andy Wood, from West Mercia Police, said: "The youth and his mother have been left quite shocked by this and the fact it happened so fast.
"It took less than 10 seconds from the man being spotted near the house to the car being reversed off the drive.
"Other people living nearby had apparently gone back into their houses leaving their cars unattended while warming up and any of them could have had their vehicles taken."
Am earlier driveway theft took place in School Lane, Hagley, at 0750 GMT when a black VW Polo Sport, registration BT5 4EUY, was stolen after being left with the engine running to warm up.
And in Kidderminster a silver VW Sharan people carrier, registration AB55 DLB, was taken in Kendalwood Road just before a mother went on the school run.
Anyone with information was urged to contact West Mercia Police.