On May 31, 2011, about 1215 Pacific daylight time, a Boeing 757-222, N526UA, operating as flight number 840, was being pushed back from the gate at the Los Angeles International Airport (LAX), Los Angeles, California, when, one of its nose wheel tires made contact with and trapped a ground crewmember's foot. The airplane's nose gear tire sustained minor damage while the ground crewmember sustained a serious foot injury. United Airlines was operating the domestic passenger flight from Los Angeles to Chicago, Illinois, under the provisions of Title 14 Code of Federal regulations Part 121. There were 182 passengers on board, along with six cabin crewmembers and two airline transport certificated pilots. Representatives from United Airlines reported the accident occurred as the airplane was being turned to a nose out position in the alley, adjacent to the dispatch gate. The tow bar's shear pins broke during the turn, and additional ground personnel arrived on scene to assist in removing the tow bar and its respective pins. The position of the tow bar was about at an 80 degree angle, but not past the limit, as marked on the airplane nose landing gear door. The flight crew was requested to set the brakes and attempts to release the tow bar from the tractor and airplane were initially unsuccessful. Proper company tow bar removal procedures for abnormal conditions were not referenced by ground personnel during these efforts. In an attempt to relieve tension on the tow bar, ground personnel requested the flight crew to release the parking brakes. Although, the company flight manual has a caution for flight crews not to release the parking brakes to assist in releasing a stuck tow bar, the flight crew complied with the ground crew’s request. The flight crew assumed they were resuming the pushback since they were not made aware of any difficulty in removing the tow bar. The airplane brakes were released while ground personnel attempted to release the tow bar. Attempts to open the locking handle on the tow bar were successful and the tow bar immediately dropped to the ramp. The airplane rolled slightly forward and overran the tow bar and then made contact with and trapped one of the assisting ground personnel's foot before coming to a stop. Post accident inspection revealed no mechanical discrepancies in the airplane braking system.