On June 16, 2011 at approximately 1758 pacific daylight time, United flight 818, a Boeing 757-200, registration N571UA, was substantially damaged during initial pushback from gate 73 at San Francisco International Airport (SFO), San Francisco, California. There were no injuries to the 188 passengers and crew onboard. The flight was a regularly scheduled domestic passenger flight from SFO to Chicago O'Hare International Airport, Chicago, Illinois. United representatives reported that normal passenger and crew boarding was accomplished using door 2L. The passenger loading bridge (PLB) operator stated she was in position at the loading bridge controls and was prepared to retract the bridge. She reported that the airplane door was closed and the loading bridge canopy was retracted. The PLB operator stated she was waiting for hand signal guidance from the ramp personnel to retract the bridge from the airplane. The PLB operator stated the signal to retract the bridge from the airplane was not received, however, the ramp personnel proceeded to push back the airplane. The ramp employee responsible for the airplane pushback reported that he heard the PLB bell ringing for about one minute, which he thought was enough time for the jetway to be cleared from the airplane. He reported that he then removed the chalks, received clearance from the flight crew, and then commenced to push back the airplane. As a result of the impact with the jetway, the airplane received a 38 inch x 8.5 inch hole in the fuselage between Fuselage Station (FS) 490 and FS 528 and stringer S-17L and S-18L resulting in damage to frame assemblies and stringers in this area.