“Fault” is premised on the issue of “wrongdoing”.
Wrongdoing: Doing something that you should not, or not doing something that you should.
So, the above heading suggests a 3 vehicle accident. Who are the wrongdoers?
Car #1 was stopped, and hit when you were pushed into it. Did nothing wrong. No fault.
Car #2 was slowing or stopped, hit from behind and pushed into Car #1. Did nothing wrong. No fault.
Car #3 did not slow/stop in time, hit Car #2 and pushed into Car #1. Wrongdoing: Not paying attention, too fast for traffic conditions, unsafe speed, not enough following distance, texting (?), etc…
Car #3 is at fault. However…..
It is very common for Car #3 driver to lie to try to push fault onto Car #2 )”Oh, Car #2 hit Car #1 first, then I hit Car #2). Just beware of this.