Both men were in possession of weapons and victim Andrew Gardner, 41, suffered fatal stab wound during the altercation with LeSean Williams.
Mr Gardner died in hospital a short time later after arguing with Williams about distressing comments made about a friend's appearance.
Williams, 19, pleaded guilty to the manslaughter of Mr Gardner, in Alexandra Road, Handsworth, where they both lived on September 18 last year.
The friend, who was living with Mr Gardner, had complained that Williams had made fun of a facial disfigurement, causing him to be distressed.
The victim had confronted Williams, who stabbed him in the chest.
West Midlands Police said Williams fled the area on an electric scooter while the victim collapsed as he returned home. Despite efforts to save him Mr Gardner died.
Detective Inspector Michelle Thurgood, from the force's homicide unit, said: “This is a terribly sad case where a man has lost his life defending his friend.
"His family had described him as ‘caring’ and told us at the time of his death: 'His passing will leave a big hole in our lives, but he will be forever in our hearts'.”
Williams pleaded guilty to manslaughter at Birmingham Crown Court on Monday. He will be sentenced on May 19.