(SAN FRANCISCO) — Police are looking for a man who approached another man from behind and stabbed him with a knife before running off, San Francisco investigators said on Friday.

The attack happened at about 3:30 p.m. on Thursday in the city’s United Nations Plaza.

Investigators say the 58-year-old victim was stabbed in the leg. Emergency crews brought him to San Francisco General Hospital with injuries not considered life-threatening, according to police.

It’s unclear why the man was stabbed. The motive remains under investigation, police said.