I don't understand these two sentences

I believe "disallowed the batting box" means that they will not mark the area where the batter stands in a baseball game. I'd need more context to be sure.

A pendulum is something that swings back and forth, typically under an old-style clock. It is a symbol for policies that swing from one extreme to another, often from very permissive to very restrictive. The author is saying that we should all try to stop the pendulum "at its mid-point" which is where most people would say we've managed a good balance between the extremes - in this case, safety of the players and their enjoyment of the game.

Thanks!
There's no other relevant information about the batting box, the following sentence is:" Now the airlines can't serve peanuts for fear of being sued by a peanut-allergic passenger."

I would ignore anything the person that wrote that sentence says. Little League has NOT disallowed the batting box. The batting box is where the person batting stands when he is at bat. That box is still in little league. A person standing in that box can't be hit by any bat other than the one he is holding in his hands since he is the one that would fling the bat.

As to the meaning of "disallowed the batting box", it would mean they no longer allow it to exist. It is not allowed.

Little League doesn't allow on-deck batters who would be in an on-deck circle.