Police are appealing for information after a serious assault on a 15-year-old boy in west London.
The victim was chased along Beethoven Street, Kilburn, by a group of teenagers at about 1630 BST.
He was then beaten by the group and it is believed his head was stamped on. The attackers then fled in different directions, some on bikes, others by foot.
The victim is now in hospital in a critical but stable condition.
Det Sgt Alison O'Farrell, the Metropolitan Police's serious violence team, said: "This appears to have been an unprovoked attack during which the intention was to cause serious harm to the victim.
"I would urge anyone who witnessed, or knows anything about, the incident to come forward and assist this investigation."