Detectives are asking shoppers who were in Morrisons at Cortonwood Retail Park in Barnsley on Thursday night whether they witnessed an alleged attempted robbery.
At about 8pm, a 51-year-old woman was getting into her car outside the supermarket, when a man got into the front seat and reportedly threatened her with a claw hammer, before trying to steal her handbag and car keys.
The man left empty handed and got into what is described as a black people carrier.
The woman suffered minor injuries as a result of the incident.
The man is described as white, in his early 40s and of a slim build. He is thought to have been wearing a cream coloured baseball cap and jeans.
Anyone with information should call 101 quoting incident number 1035 of 19 January 2017.
Information can also be given to Crimestoppers anonymously on 0800 555111.