not sure what you mean by "someone opens their car door is hit", but usually, the person speeding is At Fault. He IS speeding afterall, which is illegal in the first place..
Disagree: It is the responsiblity of the person opening the car door to ascrtain if there is oncoming traffic and it is safe to do so. It may be YOUR contention that the oncoming car was speeding - how are you going to prove it?
The possible result (from a law enforcement perspective) - the person whose door was struck could be ticketed and (if insured) the insurance companies will probably fight it out between themselves.
The person that opens the door is at fault
I beleive, whoever's car is moving (wheel-wise), is at fault.
The person driving the vehicles fault. Should have been paying attention and be alert for anything to happen at anytime.
It is the person who opens the door. Of course it is dangerous to speed, but surely you would see a fast car coming towards you, so if you were smart, you would wait until the car has past :)
The person who opens the door.
Dextral fault movements involve horizontal displacement where the right side of the fault moves horizontally relative to the left side. Sinistral fault movements involve horizontal displacement where the left side of the fault moves horizontally relative to the right side. These movements are determined based on the direction of horizontal displacement across the fault plane.
Virtually ANY time a vehicle door opens into moving traffic it will be the responsibility/fault of the party who was in control of the door. The questioner states that they were CLOSING the door??? That may be their story, but it will probably be difficult proving it.
driver of parked vehicle
the person who opened the door
This is not as obvious as you may think, because it also depends on timing. If a car opens its door when another car is approaching, that is irresponsible. But if the door is already open and then a car approaches and fails to stop, that is also irresponsible. So either one could be at fault.
When someone opens the door.
Going ONLY by the information disclosed in the question - it would appear that the person who opend their door is at fault.