You may be surprised by what background checks reveal about your umpires. As a long time assignor, I got to know the backgrounds of the people that worked for us and I'll bet that I didn't know the half of it. The head assignor and I guessed that up to 10% of our umpires had criminal records of some kind. We were aware of convicted sex offenders in the ranks.
I've made this observation before: What better place to have a sex offender work than with 9-15 players from each team watching everything that he does plus 3 coaches from each team, and a couple of dozen fans thrown in as a bonus? That doesn't even count the woman running the snack bar who never misses anything.
This is where you need a union. A union will foist this expense over on the schools, or make sure that no umpires show up for any games if the schools refuse to pay.
Peter