They trespassed the kid, so the police had no choice but to escort him out. Which absolutely is a waste of police resources, but is also perfectly legal and follows the process.

In more reasonable countries, nobody can trespass you from a football field, unless you give them a very good reason like repeated physical assault.

And followed up with a ticket. This happened at work when some teen tried to fax and couldnt figure out dialing out over 9 or 1. Somehow faxed 9911Xxxxxx so the fax called the police. They showed up and fined us for the waste of time.