Imagine, if you will, four powerful legs swinging and ripping at you with the claws shown in the picture. Play dead and they’ll carefully tear off chunks of you to eat, not wanting to disturb your “nap”. Punch ’em in the nose with all you’ve got and they won’t be careful about tearing your chunks off.
Extreme power firearms would be the only way to counter a grizzly attack.
Back in the 60’s there was a big push for hikers/backpackers to wear a bell on their gear so that they made jingling sounds when walking and this was supposed to scare the bears away. A dark “joke” among the rangers was, “Do you know how to tell the difference between black bear and grizzly dung?”
Answer: The grizzly dung has bells scattered through it and smells strongly of pepper spray.