A security guard was injured while detaining a man in Market Place, Mansfield, following the robbery at Betfred at about 11.15am today.
He was taken to hospital but his injuries are not believed to be serious.
Officers arrested a 44-year-old man on suspicion of robbery and wounding with intent in connection with the incident.
Shortly before 3pm, staff at the bookmakers were closing the store early. No members of staff made a comment in relation to the robbery.
A sign on the door simply said: “Due to unforeseen circumstances we are closed until further notice. Sorry.”
One trader at the scene said: “It is a surprise. We didn’t see anything really, just a lot of police activity around the corner.
“It is a shock that this happened.”