A 22-year-old woman was assaulted Saturday while trying to stop a robber in the University area, police said.

The unidentified man entered a business at about 5 p.m., wielded a dangerous instrument, and demanded money from the woman who was working as a clerk, police said.

The suspect allegedly assaulted the clerk when she ran after him as he was leaving the scene.

Police opened a first-degree robbery investigation.