Police have arrested two suspects in the attack, which occurred at about 10 p.m. at Hillcrest Park, near Olivera Road and Grant Street.
Police said the victim was with a group of people at the park when two male suspects approached them and tried to rob them of their car and belongings.
During the confrontation, the suspects attacked the victim, who suffered injuries to his upper torso. He was taken to John Muir Medical Center in Concord, where he died.
Police searched the area and found the two suspects several blocks from the park. They were identified as the attackers and were taken into custody.
The suspects, an adult and a juvenile, were booked on charges of attempted carjacking, attempted robbery and carjacking, police said.
Anyone with information about the case is asked to call major crimes unit Detective Mike Kindorf at (925) 603-5857. Those wishing to remain anonymous can call the Police Department's tip line at (925) 603-5836.