A woman reported being assaulted at 11 p.m. at her apartment building, just north of North Sheffield and West Armitage Avenues.
The attacker allegedly pushed the victim into the lobby of her building, where she screamed and fought him off until he ran away, police said.
Police have released a suspect sketch and describe the man as white or Hispanic with a dark complexion and short buzzed hair, 19 to 23 years old, 5 feet 6 inches, and 190 pounds.
He was last seen wearing a long white T-shirt, long shorts, and dark gym shoes, said police.
Authorities ask that anyone with information call Area 3 detectives at 312-744-8261.