The fouling in the barrel should also aid the ball staying on top the charge - and granted it would depend on the circumstances you would find yourself in whether or not you'd have time to ram something down on top the ball regardless if rifled or smooth bore. I mentioned leafs as my mind pictured Kenton in an eastern woods setting.
I too have read accounts about hunting buffalo from the back of a galloping horse such as been mentioned... In the end, one does what one needs to do to get your food, or save your life from a wild animal, or keep your hair on your head...
I also agree with Kees,
And if it got too close it was time for the tomahawk!
One last thing I want to mention after reading Uncle Russ' post, which got me to thinking,,, I don't know if it would even be possible for a "todays" muzzleloading barrel to blow with a bare ball load if the bare ball rolled forward in the bore... After-all, the undersized ball is not really obstructing the gasses from the powder charge as those gasses build (but at the same time) they should also be "being blown" past that undersized ball. Now with the old barrels our ancestors used - the way those barrels were made may very well present a questionable out come.