Um yeah, what's your point. Ippo had specifically trained his body before that fight to basically put all his strength into 1 single punch. The dude he was fighting has just knocked him off balance to the point he was standing on 1 leg. When ippo regained his balance he swung his foot back down on the mat and combined that forward momentum with the full thrust of his body and delivered it at a guy who was completely open and unable to guard. How is any of that not totally legitimate. There have been plenty of boxers in the past that have gotten 1 hit KO's on opponents, with punches that weren't even half as good as what was shown.
I'll just leave this here.