The brave passer-by intervened after what was the first of two armed robberies at Black Country convenience stores on Monday.
They chased after two men who had held up a One Stop shop in Tipton armed with a hammer and what is believed to have been a gun.
The men fled on a motorbike but were forced to throw the bag full of cash they'd just stolen into the road as they were chased down by the passer-by.
The raid happened at the One Stop store next to the Family Honour Tattoo Studio on the corner of Horseley Road and Alexandra Road just before 10am
Nine hours later, two armed robbers threatened staff at a Tesco Express in Wolverhampton before stealing alcohol, cigarettes and cash.
Police said they are keeping an open mind regarding whether the two shop raids are linked.
Officers investigating the raids were also at residential cul-de-sac Arlidge Close in Bilston on Tuesday morning.
A spokeswoman for West Midlands Police said: "Two masked men entered the store and demanded cash after threatening staff with a suspected gun and a hammer.
"They left on a motorbike, but threw a bag full of cash they had stolen in a nearby road, after a member of the public intervened and drove after them.
"Enquiries continue and anyone with information is asked to contact us via Live Chat at www.west-midlands.police.uk between 8am and midnight, or call 101 anytime.
"To remain anonymous please call Crimestoppers on 0800 555 111. Quote log number 661 of 11 November."