Police say a suspect, known only as Greg, showed up at the home and confronted the man that lived there, 53-year-old Paul Braun.
The disagreement turned physical, and during the struggle, one of the men pulled a handgun belonging to Braun.
At some point, authorities say Greg fired that weapon, and the bullet grazed the forehead of 49-year-old Dean Vanourney, who also lives there.
Greg then took off with the weapon.
Vanourney refused medical treatment, and no one else was injured in the fight.
Anyone with any information on the whereabouts of the suspect is asked to call Simi Valley police, at (805) 583-6950.