What is a batter rule?

Answer 1

Many little leagues play a 9th batter rule. At the coach/machine pitch level our league plays that when the 9th batter comes to the plate, the hitting team must announce it or he's out after a pitch is thrown. Once announced, there are automatically two outs. That batter completes his at-bat, either safe or out and then the half-inning ends.

For our Minors (kid-pitch) kids, same rules, except the 9th batter can stay on the bases and advance until he scores. When he crosses the plate or an out is made the inning ends. The only way runners behind him can score is on an over-the-fence home-run.

Answer 2

A batter rule is an instrument consisting of a rule or frame and a plumb line, by which the batter or slope of a wall is regulated in building.