When can a pitcher legally step backward off the pitcher's plate in the windup position?

A pitcher can legally step backward off the pitcher's plate in the windup position at any time before the windup begins. This action allows the pitcher to adjust their positioning without being penalized for illegal motion. The windup is defined as the start of the motion toward delivering the pitch, and stepping back prior to that point is permissible.

In contrast, stepping backward after the windup has started, or during the process of delivering a pitch, would lead to violations, as this signifies an illegal motion during that critical phase. Observing base runners does not restrict the pitcher's ability to step back, as this movement is solely dependent on the windup status, rather than situational context. This flexibility before the windup allows the pitcher to prepare and adjust as needed, which is an important aspect of the game.