The man was walking with his brother on an elevated walkway when he fell onto the sidewalk below.
"Multiple independent witnesses indicated he appeared to be intoxicated prior to his fall," the San Francisco police said.
The fatal fall occurred just after kickoff around 1:30 p.m. Witnesses gave the man first aid until an ambulance arrived, but the man was declared dead from his injuries.
The man's identity has not been released.
This is not the first time a fan has died from falling at a major sports event. In August, a 30-year-old baseball fan died after falling from an upper level at Atlanta's Turner Field during a Phillies-Braves game.
In September, 2012, a 20-year-old Tennessee fan died after falling 45-feet at Atlanta's Georgia Dome during a college football fame.
At a baseball game in July 2011, a 39-year-old firefighter died after falling about 20-feet while trying to catch a ball at a Texas Rangers game.