Worked in Yellowstone for a summer.

Spent some time with the rangers. They got all sorts of questions...

Like which handgun caliber would be best to defend oneself from a bear.

Essentially, the ranger broke it down stating there was a weakness in the skull about the size of a bullet that you had to hit directly to have a chance of dropping a bear with a handgun. While its coming at you and pissed/hungry.

So essentially, you've just pissed off the bear before it gets it claws on you.

Well placed slugs from shotguns, rifle rounds, and preferably (according to the ranger in question) a tranquilizer to re-home the bear away from people. That being said, the bears are tracked to an extent and bears who show repeated behavior endangering themselves/tourists tend to be exterminated, sadly.

Hand to claw combat? Human is going down.

This is why in the past, when bears were hunted, they were hunted in their dens during hibernation - at the end of spears to keep that hungry bear as far away as possible from your soft easily rent flesh.