Take another look at the passage:
Whenever Coach Moody sees behavior that she doesn't like—either on or off the court. The members of the girls' basketball team pay during the next practice. When Frankie was caught smooching her boyfriend Larry in the hallway, everyone had to run two extra miles that afternoon.
You chose the second part, The members of the girls' basketball team pay during the next practice. This part has a main clause: members is the subject; pay is the verb. A fragment will not have a main clause.