Video shows a man stomp on teen's bike after authorities said he knocked the boy off the bike and punched him in a frightening attack in Santa Clarita .

The ambush was reported Wednesday along the San Francisquito Trail. The man, seen on video recorded by the teen, also slashed the boy's bike tires, the sheriff's department said .

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The man was riding a bike when he assaulted the boy, who can be seen in the video waving his hands as he desperately called to drivers for help.

"He's screaming for help. In the street, waving cars down because no one had helped," said mother Lalania Bidwell. "I could hear the fear. I'm heartbroken for him."

The boy said the man, biking south on the trail, was armed with a knife. He

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