Four would-be thieves fled empty handed after the woman intervened in Northampton, England. They were arrested a short time later, the Northampton Chronicle and Echo reported. Two others are being sought.
Ann Timson, a retired market trader, was chatting across the street from Michael Jones Jewelers when she saw a group of men on scooters approach the shop.
"At first I thought one of them was being set upon by three others," she told the Chronicle. "I was not going to stand by and watch somebody take a beating or worse so I tried to intervene."
The robbers, who were carrying sledgehammers, tried to smash the jewelry store's display windows in broad daylight to steal Rolex watches.
"I didn't know what happened next but I just kept swinging my bag. They then tried to escape. I landed several blows against one lad on the back of a bike and brought him to the ground," she said.
"He raised a hammer to me so I just kept hitting out and shouting and shouting for others to help and bring them down."
The entire incident was captured on camera by a man who was filming a documentary nearby.
"The shop was behind me and when it happened I just went into cameraman mode," said cameraman Ben Jacobson. "All I was thinking was getting it framed, getting it in focus, so when the police asked me later about what happened I had to look at the video to remember it."
The jewelry store manager, Luke Allebone, told how he spotted a "chap come to the window."
"He had a motorcycle helmet on and he had a large hammer and he just started bashing away at the Rolex window," Allebeone told the Chronicle. "We could hear more of them hitting the windows so we put the shutters down and our security procedures started."
Four men were later arrested in connection with the incident, police said.