Generally speaking, the police do not have an actionable duty to protect you from third party violence. It is only where they promise help and don't deliver, or by their own action create the risk, that they can be sued. If it were otherwise, then every person who gets victimized by someone else could sue the police and claim that it was their fault because the police did not do enough to protect them.
A domestic violence victim who gets abused could point to prior instances and say "You should have arrested him." A store owner could say, "You knew there would be riots so you are at fault for any damage caused by anyone," or "the guy who looted my store should have been arrested before then."
While it is the job, and the duty of the police, to protect, that is a duty they owe to the public as a whole, not one person. Their negligence is only actionable when their own actions cause the risk.