If a pitcher throws the ball into the stands after stepping off the pitcher's plate, how far can R1 advance?

When a pitcher throws the ball into the stands after stepping off the pitcher's plate, this action is classified as a throw that results in a dead ball situation. In this scenario, the runners are awarded two bases from their position at the time of the pitch, meaning R1 can advance two bases from where they were when the pitcher released the ball.

This aligns with the rules governing pitcher throws resulting in dead ball situations, which specifically allow for such advancements when the ball is thrown out of play. Consequently, R1's advancement is justified by the rule that provides two bases from the point of release, thereby supporting the assertion that the correct answer is that R1 can advance two bases from their position when the throw left the pitcher's hand.