A 12-year-old boy faces skin grafts and having a metal plate inserted in his arm after being savaged by a frenzied dog while playing football with friends in a field.

Sean Young was bitten 23 times by the Staffordshire bull terrier and was only saved when passing workmen pulled the dog off him and pinned it to the ground for 20 minutes.

The dog was put down on the spot when a vet reached the scene.

Sean, of Boynston Grove, Sedgefield, County Durham, was playing football with friends in the village of Coxhoe on Friday when the attack happened, although details were only released yesterday.

The dog was being walked by a woman when it spotted the youngsters.

After apparently loping around the field chasing their ball it turned vicious after Sean did a handstand on the grass.

A Durham Police spokesman said yesterday: ''At first it only chased after the ball a couple of times but when Sean performed a handstand it seemed to have the effect of upsetting the animal and sending it into a frenzy.

''The dog went for Sean and seized him by the arm, dragging him along the ground.

''Its bite was so strong it broke his right wrist and the bull terrier was only stopped when two workmen passing by in a van saw what was happening and leaped out to help."

The men who rescued Sean were C and A Pumps engineers Derek Hedley and Peter Campbell, both 36, who were heading back to their depot in Durham.

Mr Hedley said: "At first I thought the dog was merely playing with the boy, but saw the dog dragging the boy along the ground.

"The lad was screaming and hysterical and we started punching it, but it refused to let go.

"I got the choke chain off the owner and we wrapped it around its neck and strangled it for about 30 seconds before it released the boy, who was bleeding badly.

"The boy was really distraught and was worried he was going to lose his arm."

Sergeant Paul Etherington said: "Thanks to their quick action. the boy's injuries were prevented from being far more serious. We will be sending a formal letter of appreciation to them.

"The owners of the bull terrier have been reported for failing to keep a dog under control and a file will be sent to the Crown Prosecution Service."

Sean's mother, Denise Young, an administration worker with National Savings, said yesterday: ''If it had not happened in a public place I dread to think what the outcome could have been.

''There's no way the boys on their own could have got the dog off and I'm grateful for what Derek and Peter did.

''Sean is still suffering flashbacks and understandably is very nervous about dogs at the moment, but hopefully that will fade in time.''