The 36-year-old rapper apparently hit the 18-year-old guy for threatening and hurling racial slurs at West's girlfriend Kim Kardashian in Beverly Hills, reported People magazine.
"The named suspect was identified as Kanye West by the victim and several witnesses. Mr West had left the location prior to officers' arrival. As of this writing, BHPD detectives are conducting a follow-up investigation," the police said.
A source close to Kardashian says it was the bystander - who has not been identified - who instigated the event and threatened the reality star.
The source says a Caucasian man began yelling racial obscenities to the paparazzi and when Kardashian told him "that wasn't cool," the man began hurling abuses at her about her and West.
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"At this point Kim was seriously afraid for her life. He was going nuts. Kanye came down to help her but then the guy ran into a chiropractic office so Kim and Kanye walked in after him."
West has a history of scuffles. He is currently facing assault charges involving an attack on a photographer at LAX.