From what I've read black bear attacks are almost never over protection of a kill/of young/personal space but predatory in nature.
Grizzlies might initiate an attack over any the above and sometimes say to themselves,"Hey, I went through all this trouble so might as well eat it."
Young male grizzlies are the most apt grizzly sub set to go into predatory mode upon a encounter.
Bears habituated to garbage, being fed, ect. often are more likely to look at humans as a opportunistic food source.
Playing dead might be a good action to take if you get a grizzly on top of you. Never a good action if it is a black bear.
Bottom line. If you are in bear territory you better have defense of some type on you.

Last edited by FVA; 11/29/14. Reason: sp.