A heavily pregnant member of staff fought back as a gang of masked robbers wielding a piece of wood raided a convenience store in Mirfield.
Police praised the brave actions of the woman, who sustained minor grazes and bruising as she tried to prevent the gang from stealing the tills.
The robbery happened at about 7.30pm on Friday at the store on Shill Bank Lane, Mirfield.
Three men with their faces covered entered the shop, one armed with a piece of wood and wearing a distinctive Halloween mask.
They confronted shop staff, including the pregnant woman, who fought back. The robbers stole two tills and fled in a light blue Nissan Micra travelling in the direction of Ravensthorpe.
Detective Inspector Andrew Lockwood, of Kirklees District CID, said: “One member of staff, who is heavily pregnant, bravely tried to prevent this robbery.
"Thankfully she was not seriously injured, but the threatening and dangerous behaviour shown by the perpetrators of this robbery will not be tolerated and we have a number of enquiries ongoing to identify those involved.
“This robbery happened during the early evening and we are keen to speak to anyone who has witnessed any part of this offence or the suspects making off from the scene.”
Detectives have released CCTV stills of the robbers and their getaway car.
The suspects are all described as white males.
The first suspect is described as over 6ft tall and of stocky build.
He was wearing a black hooded jacket with the top half having a shiny, reflective black material, grey Adidas tracksuit bottoms with black stripes down the side of the leg, black Adidas trainers and a distinctive black Halloween mask.
He is described as speaking with a deep voice and Yorkshire accent.
The second suspect is described as being of slim build and wearing a matching grey hooded top and tracksuit bottoms with a ‘Gym King’ logo on the top left chest area and on the left front trouser pocket, black trainers and a balaclava.
The third suspect is described as being of average build. He was wearing a grey Adidas top with a zip down to the chest and black stripes down to the forearm, blue stonewashed jeans with a dark coloured belt and a face covering to the lower half of the face.
Anyone with information can give information to Kirklees CID by calling 101 or using the 101 Live Chat facility on the West Yorkshire Police website, quoting crime reference 13180601434.
Information can also be given to independent charity Crimestoppers anonymously by calling 0800 555 111.