I may have some false assumptions here, so correct if needed. It is said that while ATC sounds like they are "in charge" of the airspace surrounding a major airport, control and responsibility for any given airliner is (still) in the hands of the Pilot-In-Command (PIC).
What this means is that if an airliner is given instructions to do something by ATC, and they are unable (or unwilling) to follow those instructions, they are able to tell ATC they are unable and ATC has to work it out, with all of the ramifications that implies. If the ATC controller wishes, they require the crew to contact ATC by other means (the dreaded phone call, I suppose) to explain, but the fact of the matter is, the passengers are ultimatley depending on the crew to keep them safe.
Now, let's take an airliner, at the gate, readying itself for a flight. They receive a pushback and are ready to taxi. They contact ATC Ground for instructions. Ground gives them taxi instructions. Who is responsible for the safety of the aircraft at that point?
Why do I ask this, when it should be obvious, the PIC. However, visibility out of the aircraft is limited, especially in some of the larger craft. As far as I know, there is no "check the mirrors" or "objects in the rear view window may be larger than they appear." The PIC simply CANNOT see behind the aircraft, and so any ground vehicles, personnel, or other aircraft (small or large) could cause an accident, which would be out of the control of the PIC.