What is the ruling when a pitcher drops his pitching hand to his side and stops after stepping onto the pitcher's plate with runners on base?

In this scenario, the correct ruling is that it constitutes a balk, resulting in all runners being awarded the next base. When the pitcher steps onto the pitcher's plate and then drops his hand to the side without delivering a pitch, it is considered an illegal motion. This action can be interpreted as an attempt to deceive the baserunners, which is a key factor in defining a balk.

A balk is called to maintain fairness and prevent pitchers from using deceptive tactics that could disrupt the flow of the game or unfairly advantage the defense. In this case, since the pitcher has made a motion that indicates an intent to deliver a pitch but then fails to do so, it triggers the balk rule. As a result, any runner on base is allowed to advance, which could include the award of home plate if third base is occupied.

Other options are not applicable because there is no situation where a dropped hand after stepping on the plate would be considered a strike or a legal move, nor is it a dead ball situation. The action clearly leads to a balk, which is why ruling it as such aligns with the established rules of the game.