Task: Question Answering
Input (English): Passage: A childhood accident leaves Leo mute and his devout Amish mother refuses surgery. As an adult in 2035, he works as a bartender at a Berlin strip club owned by Maksim and dates cocktail waitress Naadirah. She confides in her friend Luba that she has not told Leo about her past or her desperate need for money.
After Stuart, a rowdy customer, sexually harasses Naadirah, Leo assaults him. Naadirah talks Leo down by telling him that she needs to keep her job.
Naadirah shows up at Leo's apartment and attempts to tell him about something important. Leo shows her an elaborate bed he has been carving as a present for her. Naadirah is overcome with emotion and they have sex. Elsewhere, Maksim's mobsters meet two American surgeons, Cactus Bill and Duck, who run a black-market clinic. Bill desperately wants to leave Berlin and has pressed Maksim to provide forged documents for him and his young daughter, Josie. Duck, however, enjoys living in Berlin and runs a side business where he installs implants and performs cybernetic surgery.
Stuart returns to the strip club and taunts Leo, leading to a fight and Maksim firing Leo. When he's unable to contact Naadirah, Leo asks Luba for help, but Luba refuses. An anonymous text message leads Leo to a black-market bazaar run by Stuart. Bill and Josie are there, and Bill takes Josie away as Stuart confronts Leo. Suddenly remembering that Naadirah wrote an address on his notepad a while back, Leo leaves the bazaar after using charcoal to read the imprint. 
Naadirah's address leads Leo to Oswald. When Leo expresses interest in a picture of Naadirah, Oswald assumes Leo works for Maksim's underling Nicky Simsek, who is skimming money from Maksim's prostitutes. Leo meets with Simsek, who is babysitting Josie. Leo befriends Josie and leaves the money from Oswald and a note incriminating Simsek in front of Maksim's henchmen. 
Question: Who does Leo assault?
Output (English): Stuart.