What determines whether F1's action is legal in Situation H?

In the context of the situation provided, the legality of F1's action hinges on the rule regarding the pitcher's footwork and delivery. Specifically, when F1 lifts his nonpivot foot before stopping, he is adhering to the regulations set forth for legal pitches. The act of lifting the nonpivot foot signifies a commitment to the pitch, while stopping allows him to reposition or reset before delivering the ball.

When the nonpivot foot is lifted, if F1 stops (and thus doesn't make an immediate pitch), it complies with the rules of pitching mechanics. This ensures the pitcher has a clear understanding of the rules regarding how they can engage with the pitch, especially concerning their footing and any subsequent actions.

In contrast, considerations related to stepping towards the base or pitching immediately after lifting a foot may contain nuances that could potentially break the rules. The act of throwing without lifting the foot also has specific criteria that could classify it as an illegal pitch under certain circumstances, but the focus here lies importantly on the step and stop mechanism. Thus, the crucial aspect confirming the legality of F1's action centers on the lifting of the nonpivot foot before achieving a stop, allowing for a legal pitch delivery.