A teenager was left with a broken arm after being attacked in an Oxfordshire town centre during the day.
Thames Valley Police said the incident happened in The Charter, Abingdon, on Wednesday at about 1430 GMT.
The victim was standing outside the library when he was attacked by a man and fell to the floor.
The man continued to kick the teenager in the head as a crowd gathered. The attacker ran away but was tripped by an onlooker as he fled.
Pc Neil Wathes, of Thames Valley Police, said: "This was an unprovoked attack on an innocent member of the public who has sustained a broken arm as a result of the incident.
"Lots of people would have witnessed the assault and a person in the crowd tripped the offender as he attempted to get away."
Police are appealing for witnesses.