Legal Question in Real Estate Law in Illinois

"Neighbor" issues are always a problem. Your Alderman may provide some kind of "mediation" help, but if not, then you'd be on your own. And since it is 'criminal trespass' - ie. continued trespass after telling the trespasser to leave, you could call the police - who also might help mediate. From a liability standpoint if you are willing, you could minimize the risk by having a license agreement drawn up allowing the play as long as, among other things, the neighbor provided indemnity, insurance and supervision. But short of that, or if that wound up being a problem and you had to revoke it, you're looking at having to call the police out, or to put up a fence, or to start down the path to an injunction lawsuit.