My parents signed me up for Little League one year even though I had no interest or ability in sports. I hitched a ride to practice after school with friends’ parents or older brothers, and faithfully rode my bike to games on Saturdays - which my family never attended. And it hurt really bad. I never saw other kids’ parents acting up during the games.
My son tried a few sports in local and school leagues up until his junior year of high school. We were just happy to see him out of the house and interacting with people. A few parents got a little enthusiastic but there were no big arguments or physical confrontations that I ever saw.
Completely banning all parents from games seems pretty draconian to me, but there may be individuals who deserve it.