A simple solution is to ban parents/fans from the park.
The woman who punched the umpire is banned from the park. But what does that really mean? My girls play in 25 different parks in the area, and I put on a hat and I blend in pretty well.
The woman also got fined $412 or some random amount about that much. In my head, there might be a time I'd like to punch someone and would happily pay $412 to do so. Seemed way too lenient.