Two suspects were arrested and a homicide investigation was underway, according to Kansas City Police Chief Darryl Forte's Twitter account.
Traffic leaving the stadium after the Broncos defeated the Chiefs, 35-28, was partially blocked by a parking lot crime scene.
Forte said the victim was pronounced dead after being taken to a hospital, but authorities were not immediately able to determine the cause of death.
"Multiple parties are being interviewed at police headquarters," the department reported on the chief's Twitter account.
It said the victim died after struggling with two other people.
The slaying came exactly one year after another death at the stadium, when Kansas City Chiefs linebacker Jovan Belcher killed himself in the parking lot outside the practice facility after he had killed his girlfriend, Kasandra Perkins, at their home.
PIC: @kcpolice processing crime scene at parking lot A in Arrowhead stadium @41ActionNews pic.twitter.com/EqhpDKucRs— Andres Gutierrez (@AFGutierrez) December 2, 2013