I am going to say yes, it is possible mostly because humans kill other humans with a single punch from time to time and black bears are certainly stronger.
Cupido said there are “hundreds” of documented one-punch deaths nationwide.
One-punch deaths fall even further down the list. But it happens often enough that Gunson, without pause, is able to describe precisely how a sock to the face can end a life.
“They fall over backwards and they hit the back of their head,” Gunson said. “They often end up having a skull fracture.”
However, I can find no record of it happening in Wikipedias list of fatal bear attacks in North America. From the research that I did for this answer, it seems that most bear attacks are a lot messier than a single punch kill.
On the other hand people have survived punching bears.
A Canadian man had to punch a black bear in the nose to force it outside after it followed a toddler into a British Columbia family's home.
Nelson tried to swing at the bear but missed, hitting it in the teeth. The bear hit back, scratching Nelson across the chest and face.
"I knew it would swing first with its left but it would really come with its right, because most bears are right-handed," Nelson said.
So Nelson swung a second time.
'Most bears are right-handed.'
"I had the perfect shot to take. I did an underhand and hit it right in the snout."