You don't need any real legal basis. We're talking about kids sporting events. Social pressure is often enough.

You don't want to be the reason your kids team lost. You don't want your kid getting kicked of their team for your behavior.

There is nobody to do that. And nobody to make sure they don’t just come straight back.

I doubt many refs want this responsibility, even if it were feasible. And I don't think it is feasible in most cases. For instance, how is the ref going to pick out the problem fans while also managing the game itself? And how is the ref supposed to enforce the removal?

Keep in mind these refs are often volunteers, working solo, have no official connection to the teams or field owners.

And there is a ref shortage virtually everywhere, at all levels and sports. Making it more difficult just isn't realistic.

Authorised persons can kick someone out of a park. A ref's authority stops at the pitch/ people registered with the sport's body.