On July 23, 2019, about 0048, Pacific Daylight Time, United Airlines flight 1161, N57852, a Boeing 757-324, received substantial damage during pushback. There were no injuries to the passengers or crew onboard. The regularly scheduled domestic passenger flight was operating under the provisions of 14 Code of Federal Regulations Part 121 from San Francisco International Airport (SFO), to Chicago O'Hare International Airport (ORD), Chicago, Illinois. According to the flight crew, the airplane was at gate 62 at SFO and after the door was closed and Pre-flight and Before-pushback checklists were completed, the flight crew then received clearance to push back. According to the ground crew, the pushback operation was conducted with a tug driver and a wing walker at each wing. After pushback was initiated, another airplane was towed behind the accident airplane. The tug driver stated he saw the other airplane and stopped but lost sight of the wing walker. After he thought the other airplane was clear, he started to move the airplane again, but then was signaled by the other airplane's ground crew to stop and that he had hit their airplane. Postaccident examination of the airplane revealed that the right-hand elevator outboard section had broken at the second attach fitting. Also, the right-hand horizontal stabilizer had a puncture, end cap damage and other damage to the lower skin extending about 24 to 30 inches from the outboard end.