The Los Angeles County Sheriff's Department said they received numerous calls around 4:30 p.m. from people reporting white supremacists attacking people at Stephen Sorensen Park.
Police said the men were screaming "Heil Hitler" and racial slurs -- and waving a wallet with a Confederate flag -- as they taunted and assaulted three Hispanic teens.
A family tried to intervene in the scuffle, but the white supremacists pulled out knives and threatened them, police said.
"They just started beating them up," the father of that family, who wished to remain anonymous, explained to NBC Los Angeles. "They started coming towards us, and they pulled out some knives, and they were saying they would kill us."
The men fled the park after being told police had been called, but were eventually captured.
Police are investigating the incident as a hate crime.
No one was seriously injured.
The attack came just one day after a Ku Klux Klan rally in nearby Anaheim turned violent, resulting in three counter-protesters being stabbed and two KKK members being "stomped."
Five members of the KKK who were arrested for their involvement in the Anaheim incident were released on Monday. Police said the KKK members stabbed the counter-protesters in self-defense.
Watch video, courtesy of NBC Los Angeles, below: