Police are turning to the public to find the man who punched a woman as she was dropping her daughter off at dance practice in Los Gatos on Monday.
Police released a sketch Friday of the suspect.
They said he was wearing a white t-shirt, blue jeans and a backwards white baseball cap when he attacked the woman for no apparent reason.
There is speculation the attack could be part of a disturbing prank called the "Knockout Game," where random people are attacked while someone else videotapes it.
Witnesses said the victim was injured but refused to go to the hospital.