The collision involving a motorcyclist and a paratransit van was first reported shortly before 4 p.m., and has closed all lanes on eastbound I-580 just west of 150th Avenue.
CHP Sgt. Trent Cross said it now appears that an altercation occurred between the motorcyle rider, who Cross described as a Hells Angels member, and the paratransit van driver.
The van driver is suspected of intentionally hitting the motorcyclist, who was dragged several miles under the van. The motorcyclist died of his injuries.
The case is being investigated jointly by the CHP and San Leandro police.