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In the case you mention, it is obvious that the city government (city council, Town board, or whatever) made the decision to lease the city park and baseball fields. This may have happened through the person who was put in charge of such things (Park commissioner). In any case, you should go to City Hall and find out how and when this happened. It may be helpful to get other citizens together and attend a meeting of the city government. Put this matter on the agenda under "new business" and tell the city politicians about this problem and that you VOTE! They will respond to something like that.
For right now, it is perfectly legal to lease those public areas, although it doesn't seem to be serving the greatest segment of the population of your town.