A 16-year-old youth is being questioned by police after an 11-year-old girl was indecently assaulted.
The girl was left with facial injuries following the attack in Chelmsford, Essex, on Tueday afternoon, an Essex Police spokesman said.
The attack happened as the girl was walking along a footpath across open ground at The Bringey, near Baddow Hall School in Chelmsford.
The spokesman said the girl is not a pupil at the school.
Police have appealed for witnesses and information about the attack.
"She was walking from the direction of the school towards Sandon. She was grabbed from behind by a youth riding a BMX-style cycle," said the spokesman.
"He rode off in the opposite direction towards Hall Close after the attack."