I'm not a bear expert.I had one up close and personal experience with a black bear(with injuries) in AK.
That did inspire an interest in predatory black bears.There was a (AS I recall) National Geographic documentary on fatal predatory black bear attacks.It included some footage of the victim with camera being stalked.
I have also watched video online of people being stalked by black bears.Some died.(I'm not finding these videos today.They may have been scrubbed)
Those videos put the hair on my neck up.I saw the same expression,the same movements from the bear I ended up killing .
I'm not saying bears never make a surprise sudden rush.
But I think more often they just relentlessly approach.No expression,no rush.Just observing you and closing distance. They rush when they are close,
Understand,I used a 12 ga,I killed the bear,and I'm grateful I had a gun.
But stats say bear spray is effective,and may be,in some cases,more effective than a gun.
I had time to whack my bear in the face,(he backed off)holler,and fire a warning shot(ignored) I certainly could have sprayed this bear. He just was not leaving,he was moving closer,he already bit my wife,and we were 200 river miles from the nearest road. It was time to shoot.Whether this all took 30 seconds or a minute,I could not say.
IMO,if you stumble on a cub or a kill,surprise the bear,in general,you may get a sudden ,violent reaction.If you are unaware you are being stalked,you may get the final rush.
But,IMO,when a predatory black bear wants to eat you,its a more methodical,no place to go stalk.
https://youtu.be/3P3a9zgzEgk