Glen and Levone Butts (plaintiff) were visiting their good friends, Lloyd and Georgia Weisz (defendants) when Glen took a deadly fall down a basement stairwell. No one saw him fall. The stairwell was dimly lit and had a single dangerous step, but Glen had navigated it many times in the hours before he fell. Levone sued the Weiszes for negligence and retained an expert prepared to testify that the dim lighting and dangerous step caused Glen’s fall. The court excluded that testimony as lacking the necessary basis for expert opinions under Federal Rule of Evidence 702 and allowed the expert to opine only that a single dangerous step might cause a person to trip and fall. The Weiszes requested summary judgment, arguing that there was no evidence showing that the single step or dim lighting caused Glen’s fall. The trial court granted summary judgment and dismissed the case for lack of causation. Levone appealed.