For clarity, police protect society as a whole, by reducing the number of predators in the community and lowering rate of crime (thereby reducing the ODDS that any one citizen will be a victim of crime.
Police are not able to prevent any specific crime from occurring, and cannot help you when you are faced with an attacker. The crime will be long over, and the outcome long determined, before the police arrive.
We will do a great investigation, and quite likely catch the criminal and put them in jail, thereby protecting the people who would have been that predator's future victims.
The only person who can protect you is you. I am a retired cop, and I know that 911 is what you call after the thing is over.