A 14-year-old boy allegedly threw a knife at his girlfriend and missed, hitting a bystander at Perth train station on the weekend.
Detectives are calling for witnesses to the incident, which happened about 4pm on Saturday.
Police spokeswoman Ros Weatherall said the bystander, a 37-year-old woman, was taken to Royal Perth Hospital with an ankle wound.
"It will be alleged that the boy was in an argument with this girlfriend, when he threw a fold out knife at her as she ran away," she said. "The knife instead hit the victim in the ankles as she walking along, causing her to fall to the ground.
"The alleged offender retrieved the knife and ran from the scene."
The boy is due to appear in Perth Children's Court today charged with possessing a prohibited drug and omissions causing bodily harm or danger.
Ms Weatherall said there were a lot of people in the area at the time and police would like to speak to them.
Anyone with information is asked to call Crime Stoppers on 1800 333 000.