Leading end assemblies for movable partitions may include a movable trolley, a leading structure coupled to the movable trolley, a diagonal member comprising at least one movable feature enabling the leading structure to move from an initial position to a displaced position, and at least one sensor for sensing movement of the leading structure. Movable partition systems may include a leading structure suspended from a trolley and a sensor configured to sense rotation of the leading structure relative to the trolley. Methods of operating a movable partition may include moving at least a portion of a movable partition along a path from a retracted position to an extended position, rotating a leading structure of the movable partition about a coupling, using a sensor to sense rotation of the leading structure, and ceasing movement of the movable partition in response to a signal generated by the sensor.