What is the ruling when B1 misses a pitch and the ball touches his arm?

In this scenario, when B1 misses a pitch and the ball touches his arm, the ruling is that B1 is out and the ball is dead. This situation falls under the rules governing a strike and foul balls, where the ball contacting the batter, regardless of intent, can lead to an out if it occurs in the context of a missed pitch. The act of the pitch touching B1's arm signifies that he has not successfully made contact with the ball, thus resulting in an out being called due to the rules regarding hit by pitch or interference. The ball being ruled dead indicates that no further play can occur until the situation is resolved, ensuring safety and fairness in the game.

The answer also reflects an understanding of game strategy; as B1 is out, it would prompt the next player to come up to bat, altering the dynamics of the game in that moment. This specific ruling helps maintain the flow of the game and balance between offense and defense.