Hisham Abu says the incident happened just after he opened his San Francisco store, Sam's Market, on Wednesday morning.
Abu says the man came in with a lottery ticket and became angry when he was told it wasn't a winner.
RELATED: Mega Millions $1.34B jackpot winning ticket sold at Des Plaines Speedway, lottery officials say
"He told me you sold a fake ticket, and he had a balloon in his hand, with a pin from the front, and he had a piece of wood almost one foot long," said Abu. "(He) hit the balloon with a piece of wood, and bullet goes out and it hit my shoulder."
Abu says he didn't realize he was shot until someone else told him.
The suspect is in custody and Abu says he hopes he'll stay there so he doesn't hurt anyone else.