Two juvenile boys ran into Perry Market on Perrysville Avenue shortly before 10 p.m., one of whom went behind the counter and demanded money, police said.
"He was like, 'Stay away. Give me money. Give me money,'" M.C. Hydare, the brother of the cashier, told Channel 11.
The other juvenile was stopped and held by a customer.
Investigators said that the juvenile who went behind the counter brandished a large silver knife that was more than one foot long. That's when the cashier pulled out the sword to defend himself and chase off the juveniles.
Here's the surveillance footage that shows the altercation: