The Tuesday night incident was caught on camera in the city's Uptown neighborhood.
The would-be purse snatcher was manhandled by Good Samaritans.
Eyewitness video, taken by an ABC7 producer who happened to be in the area, shows 56-year-old Herbert Kirkwood face down on the ground after 19-year-old Cherise Washington says he tried to take her stuff.
"He ripped the straps off of my purse and ran down Leland towards Racine to get away," Washington said. "As I was chasing after him, this lady with a cane, she tripped him and he fell."
Washington decided to leave the bus stop and walk to her part-time job a few blocks north at the Admiral Theatre. As she struggled with Kirkwood the student was amazed to see a guy jump out of his car and run the suspect down.
"This guy had slammed on his brakes in the middle of the street and left his car there," said Washington. "He got out of the car and chased him and tackled the guy down and pinned him down, and then, by that time everybody was surrounding him. An off-duty police officer from California -- he used to be a police officer -- detained him."
Adel Shaw, the owner of Spoil Me Hair Salon on the corner of Leland and Broadway, saw the incident unfold.
"It's really alarming," said Shaw. "But we live in the city, and so we see this from time to time. It stresses you out a little bit."
Kirkwood has been charged with one count of felony robbery.
As a girl, Washington said her father taught her to stand up for herself, training she says just kicked in.
"I only had $20 in the purse. It was really about the principle," said Washington. "I feel like a piece of my dignity would have been gone if he took my purse and got away with it."