The fan, a man in his early 20s, was in critical but stable condition at Highland Hospital in Oakland, authorities said. He fell from the second deck to the first deck, apparently after another fan pushed him, Oakland police spokeswoman Officer Johnna Watson said.
It was not known what started the fight, which began after the Warriors loss to the Cavaliers in a tense Game 7 of the NBA Finals.
Police were interviewing witnesses and reviewing surveillance footage late Sunday. No arrests were made as of 9:30 p.m.
Any witnesses to the fight are asked to contact the Oakland Police Department's Assault Unit at 510-238-3426.
Please follow us on Twitter for exclusive stories, Like us on Facebook, Or return home for award winning writing.