Yishmael Q. Sneed, 28, was a passenger in a car driven by Derrick L. Flynn, 39, of Dixon.
The two men got into a fight, and Sneed jumped or rolled from the vehicle, police said in a news release.
They responded to the 1200 block of Palmyra Road around 1:30 a.m. on a report of a man injured in a traffic incident. Sneed was taken to KSB Hospital, were he died shortly after, the release said.
An autopsy was conducted Monday; the results were not released.
Flynn is charged with aggravated battery and obstructing justice, both felonies, and with misdemeanor DUI and domestic battery.
He refused a blood draw at the hospital, which is where the obstruction charge comes from, Chief Steve Howell said.
Aggravated battery carries two to five years in prison, obstructing justice one to four years.