The security guard was treated for non-life-threatening injuries.
Authorities are investigating a stabbing of a security guard inside a Metrolink train near Acton on Sunday night, police said.
The stabbing happened around 9:30 p.m. just before arriving at the Acton Metrolink station.
The security guard was able to subdue the suspect with pepper spray and the help of the doctor.
Deputies made an arrest and the Antelope Valley 285 Train departed en route to its destination in Lancaster.
The security guard was treated for non-life-threatening injuries.