Boulder police are asking people who were involved in or witnessed a fight at a University Hill house party Saturday to contact investigators.

Police are working to figure out what happened in the altercation, during which at least one man was injured.

The incident took place at 2:40 a.m. Saturday in the 900 block of Pennsylvania Avenue, according to a police news release.

Several roommates were hosting a house party when four unknown men who had not been invited entered the residence, police said. The residents asked the men to leave, but they refused, and one of the roommates began fighting with two of the uninvited men.

The fight spilled out into the street, and two of those involved fell into a mud-filled drainage culvert, police said. At least one man was injured in the fall.

Detectives want to speak with the other men involved.

One of the unidentified men is described as white, about 6 feet tall with a muscular build, a shaved head and two chipped front teeth, according to police.

Another is described as white, 6 feet tall with blonde, shoulder-length hair.

Anyone with information about the incident is asked to contact Detective Jeremy Frezen at 303-441-1890. Those who want to remain anonymous can contact Crime Stoppers at 800-222-TIPS or www.crimeshurt.com.