When do pitching regulations officially begin?

The correct choice emphasizes that pitching regulations officially begin when the batter steps into the batter's box. This moment is significant because it signals the start of the interaction between the pitcher and the batter, activating the rules of play regarding pitching.

Once the batter is in the box, the pitcher is obligated to adhere to specific rules concerning how they deliver the pitch, including regulations pertaining to the number of pitches thrown, balk calls, and the pitcher's conduct during the delivery. This interaction creates a definitive commencement point where the actions of both players come into play under the governing rules of the game, ensuring that both the pitcher and batter are prepared to engage in the contest.

Prior moments, such as the pitcher stepping on the pitcher's plate or the game starting, do not trigger the application of these regulations directly; rather, they are foundational events leading to the confrontation between the pitcher and the batter. Similarly, the catcher signaling the pitcher is part of the preparation process for the pitch, but it does not mark the official start of the pitching regulations. Thus, the interaction initiated by the batter stepping into the batter's box is crucial for defining the moment when pitching rules become applicable.