IMPORTANT: The umpire in chief has the final say on making a call during a game.
In baseball, there are lots of rules for why a strike will be called on the batter. Primarily, the strike zone is used by umpires to call strikes and balls. However, in rare situations, an automatic strike will be called the batter.
Here is a complete list of reasons an automatic strike may be called:
According to the batter's box rule, a batter must keep at least one foot inside the batter's box during his at-bat. There are a few exceptions to the batter's box rule like during a swing, a checked swing, the batter is avoiding getting hit by a pitch, a timeout is called, or a wild pitch is thrown.
In the National League, if a batter leaves the batter's box, delaying play for a second time in a game, the umpire will call an automatic strike. Depending on the league, a further consequence may be given to the batter by the league president.
An automatic strike will be called on any batter who hits the catcher with the bat while swinging. At the discretion of the umpire, a strike will be called if the swing and a miss hits the catcher on the backswing. No runners can advance on an automatic strike.