In my experience, no. He might give it a valiant effort, but don't count on it. For every story of a rooster successfully 'protecting the flock from a predator', I'll hear 10 that end with the rooster dead or him leading the flock to safety and the hen or hens at the back of the pack are dead. I think you can count on a rooster providing a measure of security as an early warning system for the flock; but as far as thinking if you have a rooster, your flock will be "safe," no.
As stated above, roosters can be of some help, but usually not enough to protect from predators. They can be great to sound off an alarm, but bodily contact with predators on the roosters part is not all common or helpful in many instances. I have a lot of predators around my area here day and night. I can't let my birds roam freely without constant supervision. So I built them a very large run where they do spend much of their time in. When I do let them free range, I keep them in a fenced off section...it's probably 100x90 feet or so. But it has plenty of trees and brush to hide or duck under should there be an aerial attack and such. But I keep close eye on them as they are outside. I never leave them alone for hours on end or I will lose them. When you free range, you have to expect you will lose some, possibly all of them unless you watch over them carefully or build them a big run to spend much of their days. Never use chicken wire, hawks will dive right through it. Use Hardware cloth, 1/2 inch is fine.