Khamzat Chimaev's lip scar is the result of a severe childhood injury. When he was just two years old, he fell down a concrete staircase in his home, which caused his lip to be ripped open, knocked out some of his teeth, and broke his nose. This injury left him with a lasting scar on his lip and a lifelong issue where he cannot breathe properly through his right nostril. Despite this significant injury and breathing difficulty, Chimaev has risen to prominence in the UFC with impressive performances. His scar has also been a target of taunts by other fighters like Conor McGregor, who mockingly called him "rat lip." However, Chimaev has used such criticism as motivation in his fighting career. The scar and the breathing limitation are part of the tough story behind his appearance and MMA success. In summary, the lip injury happened from a childhood accident, not from fighting or a congenital condition, and it continues to impact him physically to this day. Yet, his resilience has made his achievements in UFC even more remarkable.