Complex sentence: Because of the significant decrease in box office gross in its second weekend, the film sits in sixth place for the largest second-weekend drop; it is the seventh-largest drop for a film that opened as the number one film in the United States.
Split into simpler sentences: Because of the significant decrease in box office revenues in its second weekend, the film had the the sixth-largest second-weekend drop. It is the seventh-largest drop for a film that opened as the top-earning film in the United States.