I consistently read in historical accounts that natives would not consider attacking a grizzly except in groups, like 8 - 10 - 12 men. For example Lewis &Clark recorded this. It seems not to be specific to one tribe or nation, but across the board.

In one account from 1840s Canada, a British sportsman looked over an embankment and saw a grizzly sleeping below, an easy head shot. The Englishman cocked his rifle and was taking aim when he heard his native guide behind him cock his own rifle, ready to shoot the Englishman for breaking the rule.