Who is at fault when you back into a car that illegally parked?

It depends on the specific laws and regulations in the jurisdiction where the accident occurred. Generally speaking, if a vehicle is parked illegally, the parked vehicle may be considered to be at fault for the accident, as it was not properly parked and may have obstructed the roadway or caused confusion for other drivers. However, it is also important to consider whether the driver of the moving vehicle was exercising reasonable care and attention while driving, as they may have been able to avoid the accident by taking evasive action. In any case, it is always best to consult with a local attorney or legal expert to determine who may be at fault in a specific accident involving an illegally parked vehicle.