Ketchel's "knock down" of Jack Johnson looks like a fake job to me.
Johnson was already on his way down long before that punch lands. It's clear as day, even on that old grainy film.
At best, Ketchel caught him on the way down from a slip.
At worst, it was a fake KD put on a ridiculous telegraphed punch, staged by Johnson to add drama to the fight and value to the film.
Please check the film before attacking this post. You'll see I'm right.