What about the 50/50 raffle they do at baseball games? Do it for football games.
Announce it at the start of 4th quarter? Lets be honest if i get 5,000 fans to buy a raffle ticket at a football game and i could win 2,500 i probably stay if i could be the winner.
Also extra income they would get could go into the marketing and fan experience budget.
Still need something more concrete though. Maybe then do something like jump around before they announce the winner.
Got to get them hyped before someone wins the 2,500 bucks