In a rear-end collision where the car that was hit was parked, the driver who rear-ended the parked car is almost always liable. This is because they have a duty to maintain control of their vehicle and avoid collisions. Exceptions are extremely rare and would require showing that the parked car was in a significantly illegal or hazardous location that directly caused the accident (such as illegally parked in a blind intersection).
Even if the parked car was slightly over the line or not perfectly positioned, this would typically not absolve the driver who rear-ended it from liability. The responsibility rests with the moving vehicle to avoid the collision. The specifics would depend on the investigation and findings by law enforcement and insurance adjusters.
