Surveillance video captured the incident inside the store on 5th Avenue in Park Slope last Wednesday.
On the video, the robber is seen pushing the clerk away and helping himself to the cash register.
But, the clerk comes back and hits him repeatedly with a box.
The robber made off with the money and is still on the loose.
The suspect is described as a black man around 40 to 50 years old, about 6'0" tall, 205 lbs., and wearing a blue baseball cap, black snorkel 3/4 length jacket, black jeans, and black shoes.
Anyone with information in regards to this incident is asked to call Crime stoppers at 1-800-577-TIPS (8477).
You can also submit your tips by logging onto the Crime stoppers website at WWW.NYPDCRIMESTOPPERS.COM or by texting your tips to 274637 (CRIMES) and then entering TIP577.