MASKED robbers armed with a machete and iron bar punched a shopper to the floor as they fled from a Sheffield shop.
Police are investigating whether the robbery has any links with a series of similar raids at supermarkets, newsagents and convenience stores.
In the latest robbery, two masked men burst into the Co-op on Greengate Lane, High Green, as staff prepared to lock up.
The men stormed inside demanding cash as one of the workers was pulling down the metal shutters outside.
One robber jumped over the counter telling staff to hand over cash from the till while his accomplice frogmarched a shop assistant into a back room where the safe was and forced her to open it.
As the raiders fled the shop one of them struck out at a customer - knocking him to the floor with a punch to his face.
Janet Moorhouse, manageress of the shop, said: “The staff are traumatised by what happened.All they were doing was trying to earn a living so they should not have to put up with this kind of thing. They were frightened and have found it hard to come back to work.
“We all want these people caught before they do it again. A loyal customer who comes in every day was also caught up in all this and knocked to the floor.”
Det Insp Chris Singleton, of Sheffield’s Priority Crime Team, said police were keeping an open mind on whether the raid was linked to a series of others across South Yorkshire in recent months.
Among robberies being investigated are 10 committed between November 22 and January 31 which, although police do not believe all to be the work of a single gang, they suspect some could be linked.
A variety of weapons have been used including a gun, knives, metal bars and wooden bats.
Det Insp Singleton said of the latest raid: “The offenders got away with a substantial amount of cash. There were shop assistants working and a customer inside at the time who offered no threat or interference.
“On their way out one of the offenders struck out at the customer. We want any assistance we can get in terms of whether anyone saw the offenders.
“They were masked up but we have good quality CCTV.”
Police said they believe a stolen Vauxhall Zafira, taken from the Shiregreen area a few days before, was used as the getaway car.
It was found abandoned and burned out the day after the robbery.
Three men, aged 30, 34 and 36, were arrested and quizzed over the weekend in connection with the raid, at 9.30pm on Saturday, before being released on bail pending further enquiries.
n Anyone with information should call South Yorkshire Police on 0114 220 2020