Final answer:
The passerby who pulled the woman down from the railing may be legally liable for causing her cracked rib.
Step-by-step explanation:
The passerby who grabbed the woman and pulled her down from the railing of the observation deck may be legally liable for causing her cracked rib. In the context of tort law, the passerby's actions could be considered as an intentional tort, specifically battery. Battery occurs when there is an intentional harmful or offensive contact with another person without their consent. In this case, the passerby forcefully pulled the woman down, causing her to sustain a cracked rib.