It’s been a staple of video game boxing, that knocking down the opponent 3 times in one round results results in a win by TKO. An occasional variant is a certain number of knockdowns in the fight (3 for Super Punch-Out, 4 for Black And Bruised, anywhere from 1-10 for Ready 2 Rumble). In fact, the last game I know of that didn’t have this in some form was 1985’s Ring King. Even now, it’s far more common for a match to end this way than the usual definition of a technical knockout, i.e. one fighter is clearly out of it, so the referee stops the fight to spare him needless harm.
But for the life of me, I can’t recall a single actual bout that ended like this. Some places don’t have the rule all, and it’s rare for even a badly overmatched opponent to hit the deck more than twice in a round. (The era of Dempsey vs. Firpo-esque smashfests is long gone.) Typically, if someone hits the deck too many times or gets completely flattened once or twice without being able to answer, the ref will do the honorable thing; there’s no magic number.
Still, even if it’s extraordinarily rare, it must have happened somewhere. Like the “Golden Goal” (just the one!). Anyone?