The robbery took place at a Speedway station in Madison, Wis., at about midnight Thursday, The (Madison) Capital Times reported.
Police said the suspect entered the store and asked the clerk to make change.
"When the register was opened, the suspect partially jumped over the counter and thrust both hands into the cash drawer," police spokesman Joel DeSpain said.
The suspect grabbed just a little bit of money, the clerk told police, perhaps less than $1, before running out of the store -- losing his cap in the process.
"It's a black and gray baseball cap with the word 'Dub' on the front," DeSpain said. "Underneath the word 'Dub' it says "automotive lifestyle brand."
Police say they are looking for a black male, 21-27 years old, wearing a white T-shirt, blue jeans and white tennis shoes.