Video from Sunday's game between the Buffalo Bills and New York Jets shows the fan sliding down the 300 level railing in a seated position before flipping backward and plummeting about 30 feet to the 200 level.
He and the man he landed on were treated inside the stadium before being taken to a hospital, where they were treated and released, authorities said.
Bills President and Chief Executive Russ Brandon called the fallen fan's behaviour irresponsible and in violation of the fan code of conduct.
"This individual will not be permitted back into Ralph Wilson Stadium," Brandon said in a statement.
Season ticket-holder Jeff Savidge, of Rochester, said play on the field had stopped for a television timeout when the falling fan suddenly landed across the neck and shoulders of a man across the aisle from him.
"He kind of bounced off him and landed about two rows down on the ground," Savidge said in an interview. "I heard somebody scream from behind us, 'Oh my God!' or something like that."
The man who fell got up and said he was OK but was stopped by security from leaving, Savidge said. Arriving emergency workers put a neck brace on him and carried him away on a chair stretcher, he said.
A security officer, meanwhile, held the head of the fan who was struck to keep him from moving as he sat upright in his seat awaiting medical attention, Savidge said. He was carried out on a backboard.
"As much as it was kind of chaotic, everybody was in control," he said.
The Bills' ban on the man sliding down the railing was supported by Erie County Executive Mark Poloncarz, who said the fan "has shown that he is a danger to himself and others."
"Yesterday's reckless and dangerous incident at Ralph Wilson Stadium is an example of the type of behaviour that gives Buffalo a bad reputation and that can never be tolerated, dismissed or accepted," Poloncarz said.
The Bills lease the stadium from the county.
Brandon said the team is co-operating with an Erie County Sheriff's investigation of the incident. Sheriff's spokeswoman Mary Murray, citing the investigation, did not release the names of the men. She said charges are possible.
In September 2012, a 20-year-old fan from Tennessee died when he tumbled over a railing at the Georgia Dome and struck a man below during a college game.
Since 2003, more than two dozen cases of fans falling at stadiums have been reported across the United States, according to the Institute for the Study of Sports Incidents. The institute is part of the National Center for Spectator Sports Safety and Security, based at the University of Southern Mississippi.