In the incident involving former California Governor Arnold Schwarzenegger and a four-car accident, determining fault legally involves considering the actions and responsibilities of all parties involved. According to the details provided, Schwarzenegger ran a red turn arrow, which is a violation of traffic laws and establishes a case of negligence on his part. This act likely makes him at least partially liable for the accident.

On the other hand, Cheryl Augustine, the Prius driver, was performing a U-turn. In California, U-turns are legal in residential areas if they can be done safely without interfering with other traffic. The legality of her U-turn would depend on whether it was safe to perform at that time and whether her visibility was clear. If Augustine started her U-turn legally and without immediate hazard, she might not be at fault.

Regarding the lawsuit for “permanent disability” from a concussion sustained in the accident, Augustine’s claim of significant head trauma and a brain bleed suggests serious injuries. Given Schwarzenegger’s involvement in the accident through a traffic violation, and regardless of his celebrity and financial status, he might be seen as responsible for the damages. However, the extent of liability could be influenced by details such as Augustine’s driving action at the time of the crash and the findings of any legal investigations.

In cases involving injuries and potential negligence, settlements are often reached outside of court to avoid prolonged legal battles and public scrutiny, especially involving high-profile individuals like Schwarzenegger. This might be an attractive option for both parties to resolve the matter discreetly and swiftly. 

Overall, determining fault in traffic accidents can be complex and typically involves thorough investigations by legal and insurance professionals to assess the actions of all parties involved.