Watch that movie, Semi Pro! Just kidding... but you could hold a raffle with a great prize and advertise the raffle. You could... have some sort of contest after the game or before the game wherein someone will win a prize, i.e.; a batting contest, pitching contest, fastest runner, something to draw people to come to want to participate in the contest. Have a yard sale at the park and watch how many people will come... be sure to advertise this so word gets out. Make sure it's a big yard sale though so many will want to come.