Assign fans to a player at random. 20 players, 2000 fans = 100 fans per player. Set up sections.
Have the teams do bills and player trivia, contests, and games head to head at different stations. Each fan will do each station. If you have 20 fans per station based on the number of players, you can set a time limit at each station and cycle everyone through according to your time schedule.
The winning player's team gets autographed items from the players in attendance like 8x10s or cards or whatever.