A single punch left a 61-year-old man in critical condition in the South of Market district Friday night, police said.
The man went outside to investigate yelling and ended up in an argument with a 31-year-old man in the 300 block of Harriet Street, police said.
During the argument, the 31-year-old punched the victim. The punch sent the 61-year-old man to the ground, where he struck his head, police said.
He was rushed to San Francisco General Hospital. His head injuries were life-threatening, police said.
The 31-year-old man was taken into custody.
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