A young supermarket worker has been left with a head injury after a violent encounter with a group of alleged shoplifters in Perth’s south. Mandurah detectives are investigating the disturbing incident, which unfolded about 5pm on Sunday at the Cooloongup IGA on Ennis Avenue. Police said approximately four unknown women tried to flee the store without paying for several items. When three staff members attempted to intervene, they were assaulted by the group. “A 22-year-old female staff member was struck in the head with a glass jar, causing a laceration that required medical treatment,” a WA Police spokesperson said.